Training and development in sport officials: A systematic review

Sport officials make significant contributions to organized sport, yet scientific evidence to inform their specialized training and education at various levels has lagged. While psychological and performance demands of expert sport officials have been well documented, the extent of research about talent and expertise development, training efficacy, and broader developmental trajectories is unclear. This systematic review summarizes 30 years of published findings on the study of training and development of sport officials, including areas of research interest, study designs, and sport official characteristics. A PRISMA systematic review was conducted, utilizing three scientific databases (Web of Science, SportsDiscus, PsycInfo) to identify relevant studies (N = 27). Female participants were generally underrepresented in studies (17%), while football officials were most often represented (79%). Training intervention (59%), retrospective (37%), and cross‐sectional comparison (22%) were the main study designs. Expert and near‐expert sport officials' training histories and responses to empirically driven isolated‐skills training represented the predominant areas of study. Sport‐specific, video‐based infraction detection tasks were the most frequently used training methods to improve perceptual‐cognitive skills for on‐field decision‐making, however, studies lacked retention measures to on‐field performance. Psychological skills training programs were found to have mixed effects and used varied criteria for measuring training efficacy. Physical training showed mainly significant effects on physiological measures and aging influences for on‐field performance. More rigorous sport‐specific evidence, assessments of training transfer, program efficacy, and macro‐developmental trajectory and milestone data are needed to inform training programs and developmental plans.


| INTRODUCTION
Sport officials (i.e., referee, umpire, judge) occupy an essential role in overseeing and adjudicating organized sport for millions of participants globally.Sport officials are individuals responsible for applying rules in sport competitions and who regulate or control competition activities. 1 Sport officials include central, assistant, and technical official roles encompassing different physical, cognitive, and interactive role demands.Because sport officials are vital contributors to the regulation and feasibility of sport, they hold an integral stake to sport society more generally.Governing sport bodies continue to seek to improve training approaches and deliberate practice programs to help officials better deal with the technical, physical and mental workloads of their performance environments. 2Improvements in athlete expertise pathways have placed increased pressure on sport officiating training structures to modernize similarly, 3 where sport official training environments can be unstructured as training programs are relatively novel and lack sport-science-supported systems. 4,5Education and training of sport officials at different levels is often challenged by limited financial (and human) resources and existing empirical evidence compared to that of athlete and coach development. 5Increased evidence-based knowledge and greater investment into sport officials' training and development is needed and would likely have broad benefits to sport. 6,7h research has been dedicated to highlighting the superior attributes, personal characteristics and skills of elite sport officials, 8,9 as well as setting the standard for the requisite abilities necessary to become an elite official.To date, empirical studies on performance skills that are important to cultivate in sport officials has grown, including perceptual-cognitive skills, 10,11 physical fitness, 12,13 intra-personal skills such as coping with stress, 14 mental resilience, 15 and self-efficacy, 16 and inter-personal skills such as effective communication and game management skills 4,17,18 and teamwork abilities. 19,20This perspective emphasizes isolating sport-specific skills officials should aim to develop and that are requisite of more optimal performance.While there is a growing body of research on the characteristics of expert officials 4,21 and influences on sport officials' performance (e.g., crowd 22 ; injury 23 ), there is substantially less known about the development of sport officials. 7,24Indeed, while there has been a proliferation of research on expert characteristics, one scoping review found less than one percent of research on football officials is actually dedicated to development (i.e., how officials' skills and characteristics change over time as a result of training and/or experience). 24There has, however, been progress in the area of sport officials' development.
An expertise model of sport official development and training has generally emerged as a primary perspective for interpreting development.One body of knowledge that has derived from an expertise model has been a deliberate practice view of sport official training. 2,25Deliberate practice, namely practice that is effortful (physically and cognitively), not immediately rewarding (personally, socially or financially) and purposefully done to improve performance, 26 has been identified as one of the primary influences on the acquisition of sport expertise. 27The quality of deliberate practice that sport officials participate in, particularly at elite levels, has improved due to the professionalization of their role. 28,29As a result, areas of training now include physical preparation, 30 nutrition, 31 vision, 32 psychological skills, 33 and decision-making skills. 34Results have shown that officials report greater relevance for such activities. 25,35An example of a high-performing football referees' deliberate practice program describes two-thirds of training hours spent on physical fitness and technical lectures, and the remaining third on video match analysis, on-field simulation, and psychological workshops and individual consultation. 2The influence of deliberate practice on expertise development is well documented, 36 however, opportunities for deliberate practice training are lamented to be largely non-existent for most sport officials. 35,37For example, while developing athletes get to practice at least a few days, developing officials do not have the luxury of weekly practices.Indeed, elite central and assistant football referees are found to accumulate just over 5,000 deliberate practice hours over an average 20-year career. 35This amount of accumulated deliberate practice is considerably less than that of elite athletes. 36itional reports find that developmental experiences for officiating skill acquisition occur outside the parameters of the deliberate practice framework.For instance, aspects of sport officials' development are suggested to occur through a 'hidden curriculum', such as match experience, experience outside sport, and informal advice from other officials and mentors. 38ch officiating experience 35,39 and prior playing experience 40 are highly relevant to their development.Officiating development models have also become more common, 1,7,41 demonstrating interest to utilize theoretical frameworks to aid development plan design.While helpful to characterize development and related factors, further testing of these models is needed and clearer theoretical guidelines should address role-and sport-specific attributes.Complicating matters is the fact that such conceptual interpretations of sport official development are varied, there is limited knowledge available about early developing sport officials' experiences, and research directed towards talent identification and development is lacking. 42Furthermore, there is limited understanding about broader macro-patterns of officials' development, as well as the impacts that skill transfer, 43 career advancement, 44 communities of practice 45 and other organizational and environmental constraints 7,46  With a scarcity of information regarding sport officials' skill and expertise progression, the purpose of this systematic review was to provide a state of the science summary of research on the training and development of sport officials, to identify dominant themes in that literature, and to identify gaps and make recommendations for future research.Because of the mixed interpretations of sport official development, 1,7,41 we view development as contributed to by both formal learning (e.g., isolated training, deliberate practice programs) 2,25 and un-mediated and informal types of learning. 40,47As such, sport official development needs to be better described,

| METHODS
A systemic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines 49  3. Empirical studies.Only primary, empirical research was the subject of the present review.This included data-driven studies (quantitative and/or qualitative).Secondary research was not included, such as other systematic reviews, meta-analyses, book chapters, conference proceedings or abstracts, or commentaries.
The strategy used three review phases: 1) a broad search of electronic databases (attending to PRISMA recommendations); 2) a search of additional sources; and 3) a researcher consensus stage.Phase 1 involved a search of three databases: Web of Science, SportDiscus, and PsycInfo with a time window from January 1990-October 2020.These databases were deemed exhaustive resources for sport official learning, development and education studies, particularly considering their frequent use in previous sport official research reviews. 24,50Two categories for search terms were used to accommodate the range of commonly-used language to describe sport officials and developmental and skill group terminologies. 1 First, role-specific descriptors of the sport officials included: 'sport official', 'sport referee', 'sport judge', 'sport umpire'.Second, concepts and descriptions central to the review topic of development were used, including: 'training', 'development', 'deliberate practice', 'expertise', 'elite', 'career', and 'talent'.
Combinations of these terminology categories were then employed in our search, for example, 'sport official' AND 'training', 'sport umpire' AND 'deliberate practice'.For Phase 2, a secondary search of external sources was conducted, such as the reference list of articles found from the database(s) search, references in books, and additional website searches (i.e., Google Scholar).Following these phases, an Excel spreadsheet was prepared to record studies' author(s), title, year of publication and abstract, and records were then sorted in order to eliminate duplicates.From the list of unique records, publications' titles and abstracts were read to discern whether the articles were written in English, concerned sport officials and their development or training, and originated from a peer-reviewed journal (i.e., 'reviews', 'commentaries', 'abstracts' or 'conference proceedings' were not included).From this reduced list, a more comprehensive evaluation occurred, which involved obtaining the full-text articles.All full-text articles were then distributed among the research team and assessed for the necessary descriptive data.Each study's author(s), publication year, study design, and main findings, along with participants' age(s), gender, sport, experience level, and role as an official were procured.Where possible, standardized effect sizes for main findings are reported.However, this was not always possible due to the descriptive and/or qualitative nature of some studies, and the absence of sufficient information in others.To ensure consistency in categorizing skill level of sport officials sampled in studies, Baker et al.'s skill taxonomy 51  Quality assessment of articles was carried out using Version 18 of the Mixed Methods Appraisal Tool (MMAT). 52This tool was designed to assess the quality of five types of empirical studies (i.e., qualitative, nonrandomized quantitative, mixed methods, randomized control trials, and quantitative descriptive studies) using five evaluative criteria per type of study.Although MMAT metrics have limited utility and should be interpreted cautiously, studies were scored from 0% (i.e., 0 out of 5 criteria met) to 100% (5 out of 5 criteria met) as a crude measure of study quality.Three reviewers assessed the quality of the papers independently for interrater reliability and scores were compared.All three reviewers came to a consensus on the final scores.

| RESULTS
Phase 1 identified 3,924 articles following database searches using keywords.An additional 19 articles were identified through external sources, totaling 3,943 articles.Removal of duplicates resulted in a total of 2,096 articles.After reviewing the titles and abstracts, 1,980 of these records were eliminated, leaving 116 studies identified for full-text evaluation.Following this comprehensive assessment, 89 articles were removed as they either did not include a training aim, utilized neither a longitudinal nor retrospective design, or sport officials were not the primary participant.This left a total of 27 articles following screening that remained in the final study selection (Figure 1 1. 17 studies received a score of 100%, five studies a score of 80%, and five more a score of 60%.

| Descriptive Results
27 articles were included in the review (see Table 1), 17 of which used short-and medium-to long-term training interventions, while ten studies used retrospective designs.Of all studies reviewed, six studies used cross-sectional data and three studies implemented longitudinal design (across one or multiple sport seasons).All studies were published within the 20-year period between 2000 and 2020 (n = 10 from 2001-2010; n = 17 from 2011-2020).The studies included in this review were predominantly comprised of samples from European countries (n = 20; 74%), inclusive of the United Kingdom, Belgium, Germany, and the Netherlands, with three studies from Australia, three from Israel, and one from the USA.The sport that had the greatest representation (in single and multiple sport studies) was football (n = 21), followed by rugby union (n = 2) and Australian rules football (n = 2).Three studies included multiple sports (an average of three sports per study and all were retrospectively designed).
In terms of sample participants' characteristics, 26 of the studies involved samples with ages of 18+ years, while studies with a sample under 18 years of age only accounted for one study.Gender of participants was primarily male, although over half of the studies (n = 15) did not report gender (although not explicitly indicated).Only five studies reported female participant samples, in which females made up 17% of the total sample for studies reporting gender.23 studies included 'expert' samples (e.g., international and national competition, professional sport league), while 'developing' officials (i.e., semi-professional, metropolitan, regional, club, senior divisional) were sampled in 14 studies (12 of the total studies reviewed included both skill groups).'Beginner' sport officials (i.e., youth, elementary school, community sport) accounted for samples in only two studies 53,54 (one of which also included 'expert' and 'developing').Eleven studies reported central officials' experience to be on average 11.7 years, while four studies reported assistant officials' experience to be 5 years, on average.Five studies reported sport officials having experience functioning in both roles and one study used number of matches officiated as a criterion for experience. 55*** Table 1 about  Of the six central official training studies, four studies yielded an average percentage accuracy improvement of 5.9% (min = 4% 56 , max = 8.4% 37 using video-based methods).One study showed an 8.1% improvement in decision accuracy in context-specific decisions compared to not, 5 while two other studies found significant differences in decision accuracy improvement between skill groups (17.4%, low-ranked developing and 3.6%, high-ranked expert officials 37 ; 8%, less-experienced and 2%, more-experienced sport officials 55 ).One study showed additional improvements in decision accuracy across different testing points following training. 55 remaining four studies examined assistant officials' response accuracy improvement on closed-skill, signal detection decision test (i.e., flag vs. no-flag errors for offside decisions in football).One main aim of training was to improve assistant referees' ability to differentiate spatial positioning in players' movements through a frame recognition task through web-based training. 57,58Three studies used video simulations and computer animation, 57,58,59 while another tested influences of video speeds on off-side decisions. 60Compared to no training, training groups mainly showed significant results, yielding 12.5% 60 to 17% 57 improvement rates in response accuracy, while some other studies showed only marginally significant 59 or no significant improvement 60 depending on training mode.For all perceptual-cognitive training studies for sport officials, decision analysis and training protocols ranged in format from webbased 57,58,61 to in-person groups 55,62 to individually completed. 37Of the four assistant official decision training studies, only one examined transfer of training to on-field performance. 57 second category, physical fitness, examined the effects of physical training programs on changing aerobic and anaerobic capacity (n = 2), and longer-term, retrospective tracking of physiological performance indicators as a consequence of instituted training programs (n = 2).
All studies were from football, and involved elite football officials.4] Most common physical output and performance measurements evaluated included max heart rate (n = 3), distance covered (n = 3), running intensity (n = 2), top running speed (n = 2), VO2 max (n = 2), blood lactate concentration (n = 2), and average distance from on-field fouls (n = 1).These measures were influenced by high-intensity intermittent training 65 and interval training 66 in both lab-based 65,66 and on-field training simulations. 64luative measures used in studies differed between on-field performance indicators 63,64 to more off-field, structured physiological tests (i.e., the Yo-Yo intensity recovery test 65,66 ; 12minute run 66 ).Two studies incorporated physical training with perceptual-cognitive testing. 5,62sical training programs for elite football officials showed significant improvements in the Yo-Yo recovery test from 31% (off-field 65 ) to 46.5% improvement (on-/off-field 66 ), while retrospective studies found no significant age effects on changes in VO2 max over time 64 .Additionally, although older officials (43-48 years of age) might experience age-related declines in physical fitness during matches compared to officials ten years younger (28.4% and 35% decreases in high intensity running and sprint count, respectively), they are found to be equally close to match play as their junior counterparts to make calls effectively (reflecting a potential ability to better adapt to fast-paced matches). 63Training was mostly performed in groups of sport officials, while one study relied on individualized training plans to be followed. 66sum, findings of the efficacy of physical training programs were generally positive, but there are indications of age-related differences on physical outputs after training. 63hird category, practice histories and macro-developmental pathways, explored domain-specific training activities and histories among sport officials (n = 8).The primary focus of these studies was on officials' engagement with deliberate practice, as well as the influence of their participation histories as athletes and officials in their sport development.Four studies documented the types of training and deliberate practice and modes of learning that officials can engage in, including their accumulated practice volumes, and the relevance of these activities to expertise development. 25,35,47,67Two studies concentrated on non-training or 'unmediated' practices that occupy important informal experiences in development. 47,68One study concerned developmental milestones/events influencing sport officials' developmental pathways, which reported that officials had non-linear developmental trajectories. 40Match-experience was frequently identified as a crucial and positive influence on expertise development. 25,35,43,68Match experience was calculated in studies based on estimated years 68 or number of matches, 55 and also operationalized match competition context ('friendly' vs. 'league' 25 ).Other developmental factors addressed in studies included specialization age into sport officiating 68 and transfer of skills to sport officiating from prior playing experience. 40,43For example, higher skill level referees started refereeing at younger ages than lower skill-level officials. 25Four of the studies used quantitative approaches to approximate previous volumes of deliberate practice hours and match experience, 25,35,67,68 two studies used qualitative methods to describe and conceptualize pathways of development, 40,43 while the one remaining study used mixed methods. 47Five of the eight studies conducted cross-sectional comparisons of sport official skill level and role.
The fourth category, psychological skills, examined the benefits of educational programs and training effects on mental skill characteristics and attributes in sport officials (n = 4).Psychological characteristics in sport officials, including self-efficacy 69,70 and mental resilience, 70,71 were the explicit focus of these training studies.Two studies trained officials' visualization skills (imagery), use of in-performance self-talk and distraction coping, and preperformance routines and plans. 70,71Three studies used multi-stage educational programs concerning psychological and performance skills, [70][71][72] while another two studies used an in-situ, within-match design. 69,700][71][72] One study showed no clear significant benefits, 69 while the remaining three studies lacked an explicit measurement criterion, instead using number and level of matches appointed, 72 assessor reports, 70,71 and officials' self-evaluations 70  focussed on developing perceptual-cognitive skills through video-based methods.Specifically, perceptual-cognitive training was found to be beneficial for lower-level skill groups, yet yielded small to nonsignificant improvements in more expert officials. 37,55While some studies provided evidence for the efficacy of training modalities, 56,58,66 others did not. 62,65,69Physiological training programs, as assessed by changes in a variety of biological 66 and physical response measures to training 65 were generally impactful.Improvement of sport officials' psychological attributes occurred through in-situ training methods 69 and through more long-term learning programs (e.g., 'mental toughness' education 70,71 ), but these and other training programs lacked longitudinal retention tests to evaluate training outcomes, sometimes relying only on qualitative feedback or performance indicators (i.e., officiating appointments 72 ).A far smaller collection of studies confirmed sport officials' consensus for the importance of match experience, 25,35,40,43,68 transfer of skills from playing sport, 40,43 and influences of other career and developmental milestones. 40,53,68Overall, there is a relatively modest number of empirical studies on sport officials' training and development, resulting in fragmented areas of research and underdeveloped representation in a diverse range of sports, skill levels, and demographics.

| Sport, skill and demographic diversity
The review found a general lack of heterogeneity in the participant samples used in studies.Reporting of participant gender was generally absent in many studies (57%; although it is highly likely that in these cases samples were male), and those studies that did report gender had limited female participants in their samples.An underrepresentation of female sport officials in empirical studies have been more broadly confirmed elsewhere, 48 and might be a consequence of few females to recruit from, as especially at elite ranks, males make up the majority of participant pools.Nonetheless, future training and development research should find ways to incorporate more female representation in studies, and explore gender differences in responses to training, training and participation milestones, and career histories, as well as barriers to successful development. 70 collective works provide foundations for developing central officials' physical preparation programs and perceptual-cognitive training tools for assistant officials in football, respectively.Deliberate practice and training histories of high-performance football official skill groups are also accounted for by MacMahon et al. 25 and Catteeuw et al. 35 Research designs and topics explored in football officials need to be replicated in different contexts and in sports where role-specific demands for officials may differ. 1,7For instance, interceptive sports (e.g., baseball) or dual sports (e.g., tennis) will each require a deeper understanding of their sport-specific training and development.Not only do different sports have different officiating demands, they can involve different dynamics between officials, and also have different implicit and explicit conventions about the enforcement of rules.
Another imbalance found in this review was that the development of non-expert sport officials was vastly unstudied.Importantly, these skill groups make up a greater volume of sport official populations, yet there is a paucity of evidence-based knowledge about developmental histories and practice volumes, and the efficacy of training programs and interventions among this population.Continued challenges of high drop-out rates and documented stressful experiences in early participation heightens a need to address their training and development supports more explicitly.Possible ancillary benefits of training novice sport officials could include improved performance, skill acquisition, self-efficacy, and stress and coping, although these require further analysis. 7

| Modelling macro-development and developmental histories
There was an emphasis in reviewed studies on testing short-term, micro-training interventions, with relatively few studies on macro-developmental (practice and training) histories, trajectories and milestones.More opportunities to participate in deliberate practice is perceived as valuable training to reach and maintain expertise levels, where more comprehensive physical preparation programs and decision-making training are found to exist. 2,35In contrast, this review showed an observed need for better understanding of milestones and developmental training and trajectory data.Development frameworks for sport officials have begun to emerge recognizing this need, 1,7,41 however, how they accommodate sport-specific requirements and characteristics of officials' advancement and turnover patterns needs further detailing.Additional research encompassing more diverse skill groups and sports is needed to inform such frameworks.More realistic impressions of patterns in sport officials' development (their development histories and milestones) could aid modelling of participation and non-elite pathways.In particular, more clarity is needed about types of development activities and experiences most beneficial to entrylevel structures in order to support the ongoing challenge of retention and talent development.As research and support programs develop, it might also be necessary to explore how development is influenced by recruitment and talent identification within sport officiating.
Eight studies were found in this review that can inform stage-based development plans by revealing some constraints on officiating development that need further insight.Past athletic history, the age of specialization as both an athlete and sport official, and officiating advancement opportunities might affect aspects of one's practice history and developmental milestones.Acquired 'experiences' as an official (matches officiated), as a player, and transfer of skills from outside sport, were non-training activities frequently identified as essential contributors to development.Notably, there are mixed reports from sport officials about the contributing effects of being a former player in rugby union 40 compared to football refereeing. 25ure research might benefit from investigating if or how playing experience contributes to early phases of learning and entry into sport officiating (e.g., motivation, knowledge of rules, fitness, predicting and reading match play, and communicating with players).Implicit forms of learning need further differentiation from formalized deliberate practice within developmental processes and at each point of development.'Unmediated' practice (e.g., peer-to-peer learnings, watching other officials, watching sport) is said to be important to learning, 47 but is generally untested in regard to how it might mediate or moderate the influence of deliberate practice.
Going forward it will useful to either test macro-developmental models or collect data that can inform the implementation of such models.Some interpretations of development observe various interconnected pathway types (to participate in sport, seek an active lifestyle, achieve expertise) and hierarchical stages sport officials' pass through based on promotion or competition level. 1 There are other suggestions of non-linear processes 40 and holistic influences on career progress. 41Mechanisms for sport official learning and development should not be arbitrarily separated from the context they occur in and should consider sport officials' backgrounds, motivations, or cultural dispositions. 46Questions remain concerning how female sport officials navigate their progression opportunities compared to their male counterparts and the degree of transparent female developmental pathways in different sport contexts. 73ressing the complexity of development for sport officials can be informed in future research through accounting for interactions among the individual, sport and environmental factors explained by a constraints-based approach. 7Based on reviewed studies, there is still great differentiation among developmental models and need for more empirical testing.Entry age into sport officiating, 68 transfer of skills, 40 and other change-events 53 encompass broader developmental influences that need to be studied in larger cross-sections of sport officials.Given the potential importance of prior participation as an athlete on officiating development, it may also be useful to consider whether or not athlete and officiating developmental plans should be mutually exclusive or conjoined.As officiating development programs continue to emerge and evolve, in-depth exploratory case studies of these programs might offer valuable insight into sport and/or organization-specific developmental processes and outcomes.

| Representativeness and transfer in decision-making training methods
Off-field, video-based training methods were the main approach used to improve perceptualcognitive skills in sport officials.A common hypothesis underpinning training studies was that off-field practices contribute to on-field, decision-making accuracy and consistency.However, only one study employed a retention test 55 and one evaluated on-field transfer. 57Studies primarily used isolated video decision situations (from 3 rd person perspective) as the mode through which to train perceptual-cognitive skills.Some training studies manipulated perceptual information presented through such video stimulus (e.g., blurred perceptual information 56 ); contextualized to matches, 5 providing opportunity for other types of video manipulation in training design (e.g., video speed 60 ); decision difficulty, 34 and visual search strategies. 74oing forward it may be useful to explore decision-making training paradigms that are more representative of actual officiating tasks.Indeed, conventional approaches for perceptualcognitive training have been critiqued as overly focused on improving proxy factors, such as vision, attention, memory, and decision-making in an isolated manner. 75Such decontextualized training approaches have been criticized for their limited representativeness of actual on-field performance demands. 46Match broadcast perspectives of decisions were commonly used as video stimuli for officials making perceptual judgements in training studies.This can possibly neglect actual perceptual cues used in competition.59] This review finds that physical demands have begun to be incorporated into perceptualcognitive training, 5,62 however, few studies embed other performance constraints within decision-making training (psychological/emotional factors, match interactions with players).
Similarly, this shifts traditional decision-making training from relying on an accurate 'standard' to more individualized approaches for improving adequacy and contextual judgements in decision-making.There is tremendous potential to incorporate 3D virtual environments 76 and computerized simulators where financial viability allows, however 360°VR has emerged as a more ecologically valid and potentially more superior training tool for officials. 77Incorporating such technology can train stronger behavioural correspondence and allow participants to reflect on their own performance or another's first-person recordings.Sport officials report greater enjoyment for such training and increased immersion in perceptual-cognitive demands, and are shown to enhance their reflection-on-action. 78 Future training studies for central officials could test use of mobile recordings of match performance and increase use of first-person views in training to increase representativeness through reinforced perception-action coupling.Testing new approaches to training sport officials' cognitive performance other than context-specific video may be an interesting challenge for future training studies.Naturally, researchers and administrators must weigh the financial costs associated with creating more representative training tools. 79ortantly, benefits of isolated perceptual-cognitive training structures in expert and near-expert skill groups were found in this review.Perceptual-cognitive skill development and training in early developing sport official skill groups could act as methods to help accelerate needed perceptual-judgment experience. 68Apart from rule knowledge and experimentation with rule application, questions remain about how sport officials can improve composite skills in their decision-making, and what progressive focuses might be relevant across officials' development phases and participation levels.A more comprehensive view of sport official development and skill acquisition might benefit from evaluating the appropriateness of different traditional and ecological pedagogies.

| Strengthening psychological skills education and performance skills training
A small number of studies (n = 4) were aimed at improving sport officials' psychological characteristics and skills to better cope with pressures of officiating participation and support performance.Training studies aimed to improve officials' self-efficacy beliefs through feedback exercises within-performance 69 and longer, more isolated resilience (or 'mental toughness') education training programs. 70,71Training activities addressed mental characteristics (e.g., concentration, 70,72 self-efficacy, [69][70][71][72] mental skills (e.g., imagery 70,72 ), coping during performance (e.g., self-talk, distraction control 69,70,72 ), pre-competition routine 70,72 , and other psychosomatic training (e.g., progressive muscle relaxation, biofeedback 70 ).Certain study variable measurements were unclear, including an indirect assessment of training efficacy, whose most common measurement criteria was selection for advancement 72 and other times officials' own self-evaluation of their mental skill performance. 70Some other studies provided more explicit theoretical underpinnings for training, 69,71 while others provided greater rigor for mental skill intervention design. 72Considering the mixed findings for training efficacy, further clarity about beneficial types of training and longer-term learning retention is required.
Other identified psychological characteristics and skills important to sport official development and performance are not always identified in training.Self-efficacy is frequently cited as important to sport official performance, motivation and commitment to the role, 80 and acts as a buffer to external pressures such as abuse.Developing support structures to improve sport officials' efficacy should consider ways task-specific efficacy (e.g., making confident and critical decisions, interacting with players, handling pressure 81 ) are addressed in training design and mastery experiences afforded to sport officials.Improving perceived organizational support, commitment, and resilience in sport officials would permit more comprehensive self-reported perceptions and efficacy in their training programs and educational support.One example is selfregulated learning processes 82 that might contribute to how readily early developing officials learn technical officiating skills and advanced officials adapt to their training demands.Selfregulated learning plays a crucial role in expert development in athletes by helping optimize their practice. 83,84Within reviewed studies, training diaries and individual or group performance reflection workshop formats were implemented [70][71][72] and reflective practices were frequently identified as vital outcomes and aspects of training. 47,71These tools were also identified as useful in the training histories of expert sport officials. 25elopment programs aimed to enhance officials' capacities to manage external stresses (e.g., deal with abuse) and emotional labor of their role were generally absent.Problem-and emotional-focused coping strategies, 14 emotional self-regulation abilities 85 (including benefits of rational emotive behavior therapy on officials' performance 86 ), distraction control and other cognitive reframing, 87 pre-match preparation, 88 and post-match debriefing 89 could constitute program testing areas worth exploration.There is evidence that sport officials can experience mental health distress and disorder at elite ranks, 90 ushering forward a need to evaluate mental health factors and education literacy programming for larger sport official populations. 91,92For example, youth participants represent vulnerable populations developing as officials where selfdetection, prevention, and management of mental health associated to their role need strengthening.Additionally, knowledge about the influence of mental health on development patterns and drop-out rates in officials is generally non-existent. 92 Over half of the reviewed studies (n = 15) focused on explicit micro-training programs to improve sport official performance.However, a number of performance-related skills were missing from reviewed studies.Communication skills are consistently linked to effective officiating performance, although this review found no explicit training intervention aimed to improve communication competencies, interactions with players and other game management education.Individual differences in communication capacities weigh on sport official evaluation, selection, and development, 93 and sometimes improving these skills are said to happen through more implicit processes. 38,40Effective body language and decision communication techniques such as [rule] explanation giving, 38,94 and higher-order interactive skills such as active listening, 8,95 social monitoring skills 17,96 and conflict management style 33 or behavioural management 97 are identified areas for development.Also, evaluating training efficacy for improving sport official teamwork processes through enhancing group cohesion 98 , shared team mental models, 19 and coordination preoccupations between central and assistant officials 20 could be sought.Different training modes, methods of learning, and training periodization to design appropriate training protocols or systems, such as in-situ forms of learning within-performance, also might help to more readily bridge off-field knowledge to in-match performance. 69

| Physical development and sport-specific fitness programming
A main emphasis on physical training of more elite football officials was found, reaffirming a lack of demographic diversity in sport official development and training research.Studies focused on training standards in expert skill groups and mitigating aging effects on footballspecific physical match performance. 63With some differences in training methods, length, and frequency identified in the review, studies mainly focused on football officials' cardiovascular fitness and strength for varying workloads and movement demands experienced in-match.

Models of high-performance approaches can aid in structuring development plans in physical
training and fitness programmes for non-expert groups and other sports.However, less is known about how officials are affected by the physical constraints and functions required of their sport and level.For example, cited differences in distance covered by officials in football have been estimated to be up to 12 km 99 but only 6 km for basketball officials. 100Also, there can be fewer requirements for physical fitness in officials from other sports. 1 With some detail of physical training programmes available, broader physical development and more sport-specific evaluation measures are missing.Knowledge about current approaches used by early developing sport officials to stay fit, when and how certain characteristics of physical training should be introduced for optimal development, and which anthropometric types and individual factors are favoured should be further investigated.Physical fitness development in sport officials can help align and contribute to evaluative standards, both progressively and representatively in sport official pathways.How physical fatigue influences sport officials' decision-making processes is not fully understood, 101 but understanding how physical fitness training is involved in the acquisition and learning of perceptual-cognitive skills could be a question for future research.

| Limitations of the review
This systematic review provides the first comprehensive synthesis of sport official training and development literature, although a few limitations should be discussed.We focused on sport official study participants, thus one possible limitation is the exclusion of other 'grey literature' possibly informative of non-official samples or perspectives (officiating developers' commentary, description and documentation of education programming approaches).Future research could distill concepts from such studies to generate dimensions of officiating education programme planning at different levels.Sport organizations might also have data on the efficacy of their training programs, accreditation testing, workshops and camps that could add to our understanding of expertise development.Additionally, the inclusion of English-language-only peer reviewed studies means that there might be evidenced-based research on the development of sport officials not captured by this review.Because the focus of this review was on development, research on tangential topics, such as injury risk and prevalence, were beyond the scope of this review.Naturally, these topics can have a moderating and/or mediating influence on training, performance, and developmental trajectories.

| Perspectives
Given training and developmental supports are paramount to sport officials' retention, talent identification, and expertise development, empirical knowledge to inform efficacious education and sport-specific development programming for sport officials is in high demand.In contrast to past scoping reviews of sport official research, 24,48 this systematic review built on our current knowledge by providing details about specific forms of isolated skills training and macrodevelopment in sport officials.The research might be useful for sport official governing bodies, administrators, and coaches in designing and planning sport-and skill-specific deliberate practice protocols, training support, and development structures.However, before specific protocols and practical recommendations can be made, additional research is needed on different sports, and officials from non-expert skill groups.

| CONCLUSIONS
The results of this systematic review draw attention to many gaps in the current body of research on the training and development of sport officials.As decision-making skills are recognized as central to sport officials' performance, it is unsurprising that perceptual-cognitive skills were a dominant focus of reviewed studies.Increased empirical evidence in sport-and role-specific aspects for developing psychological attributes, decision-making skills, and physiological capabilities in officials require further defining.Knowledge concerning non-expert, and macrodevelopmental patterns and histories of sport officials could provide important knowledge to inform and strengthen future designs of talent advancement pathways for different officiating skill groups.The associations between drop-out, self-efficacy, sport commitment and deliberate practice programs for grassroots and early developing officials are still unknown. 7,80,89In expanding on the findings in this review, we conclude that a deeper investigation into approaches to sport official learning and development processes (e.g., retention, talent identification/development) needs to be undertaken in more diverse populations, sports and  [49] .

Practice histories and macro-development pathways
Ollis et al 2006 [40] 25  Giske et al. 2016 [47] 83 (10)   Adult R, AR Football Expert; Developing Retrospective, Cross-sectional 80% Compared to sub-elite referees, elite referees showed greater use of mental skills training for visualization, concentration strategies, and self-talk.No differences were found in physical training volume and type, or unmediated learning (i.e., watching sport, informal interactions with referees, coaches).
Samuel et al. 2017 [53] 154 Adult R AR Football Beginner; Developing; Expert Retrospective, Cross-sectional 100% Professional level and role predicted rates of occurrence of change-events in referees' careers (M = 10.4,SD = 4.5).Most reported change-events were transition to a higher league (97%), excelling in a big match (86%), and a poor performance or decision error in an important match (74%).Impacts of change-events on referee pathways was influenced by openness to consult with others and use of coping strategies.
Mack et al. 2018 [43] 18 Adult R, U Mixed Expert; Developing Retrospective 100% Prior playing experience and match-officiating identified as critical activities for expertise development.
have on development.It is also essential to understand what evidence base exists on the development of sport officials.This imbalance directly impacts the fidelity and efficacy of emergent officiating training approaches and development models and plans.
detailed, and characterized to account for the myriad of influences on development.Training interventions, and retrospective and longitudinal studies between the years 1990 and 2020 were evaluated where studies must have examined or tracked changes in performance variables or developmental factors in sport officials.This review expands on previous scoping-style reviews of sport official research 24,48 by specifically targeting development and training studies of sport officials.
to examine empirical studies on sport official development and training.Studies were included in the final review if they met the following criteria: 1. Sport official participants.Only studies where sport officials were the primary participant were included in the review.Non-officials and other 'outsider' viewpoints (sport official development managers/administrators, coaches, mentors) about sport officials' training and development patterns and processes were excluded.2. Development: Time-based and/or volume-based comparison.Included studies must have tracked a training or performance variable over time.This could have been assessed by prospective or longitudinal education or training approaches, as well as short-term interventions/training studies that focus on improving a specific skill or ability (i.e., micro-training, short-term approaches).Retrospective studies of development, including developmental milestones, pathways, and training volume (i.e., macro-development) were also included.Studies that measured performance differences based solely on expertise level, or utilized an expertise-approach design to compare skills and abilities (i.e., cross-sectional comparison of skill groups), were excluded.
was used to classify samples as beginner, developing, and/or expert.Training intervention studies were classified based on their short-(<1 week), medium-(multiple weeks within one sport season), and long-term timing (one sport season or longer).Study designs were classified as cross-sectional (comparing developmental variables of different skill groups), retrospective (long-term tracking of developmental variables), and/or training interventions (evaluating impacts of training exposures on developmental variables).A series of consensus-based discussions took place amongst the research team to reach agreement for article inclusion and accuracy in descriptive data.
provides a flow diagram of the PRISMA process).*** Figure 1 about here *** The MMAT quality assessment of the 27 articles resulted in three studies being classified as Qualitative, four as Randomized Control Trials, 10 as Non-randomized Studies, eight as Quantitative Descriptive, and two studies as Mixed Method.Based on these classification categories, the MMAT Quality Scores for each study are presented in Table here *** The 27 studies included in this review were subdivided into four thematic categories according to the types of variables they examined: (i) perceptual-cognitive skills, (ii) physical fitness, (iii) psychological skills, and (iv) practice history and macro-developmental pathways.The first category, perceptual-cognitive skills, included 11 studies.All studies used video-based testing and training methods, and eight studies utilized 'mediumto long-term' training interventions ranging from 2.5 to 13 weeks in duration (mean = 6.5 weeks) involving 4 to 13 training sessions (mean = 7.7) separated by an average of five days.The remaining three studies were considered 'short-term' ranging from one to three days and averaging one training session/day.All studies demonstrated statistically significant improvements in sport officials' decision accuracy as a result of training, as measured by video-based infraction detection decision task.Seven studies assessed decision accuracy changes in central officials' subjective judgements of one-on-one player contact decisions (football, n = 3; Australian Rules football, n = 2; rugby union, n = 1) and of novice students' subjective decisions regarding player contact situations ('Swirl ball', n = 1).
to evaluate training efficacy.Qualitative feedback from sport officials indicated a general relevance for psychological skills training and its benefit to their performance. 69,724 | DISCUSSION The aim of this study was to review empirical studies on the training and development of sport officials between the years 1990 and 2020.Unexpectedly, this review found that published articles on sport official training and development only began to emerge in the early 2000s.This finding in itself illustrates the infancy of this research field and relative disparity in progress to that of athlete and sport coaching development.Overall, sport official training and development research used a variety of study designs from micro-training interventions, to longitudinal tracking of responses to training programs, and sport officials' retrospective recall of their training volume and type, including descriptions of and mediators in their developmental pathways.Studies mostly sampled high-performing and experienced sport officials, and mainly As a possible remedy, timebased tracking of stress and burnout in sport officials in relation to their developmental patterns, match-performance, commitment and motivation, and responses to training would be worthwhile.How sport officials' psycho-emotional wellbeing and mental health are associated with early specialization, skill acquisition, and talent development comprise some of the next steps in psychological skills development research.

Figure 1 :
Figure1: PRISMA flow chart showing number of citation records collected and number of eligible records after the screening process.PRISMA: Preferred Reporting ITEMS for SYSTEMATIC Reviews and Meta-Analyses[49] .
Weston et al.'s 63,64,66 and Put et al.'s referring younger than sub-elites (d = 1.02) and, as they developed, they engage in greater volumes and types of training.Competitive match refereeing was rated a significant activity for skill acquisition and refinement.experience (β= 0.46), and accumulated practice hours (β= -0.55) differentiated national vs international referees.Matches officiated and physical preparation were rated the most relevant forms of training.