Effect of a new concussion substitute rule on medical assessment of head collision events in Premier League football

TarziG, etal. Inj Prev 2022;0:1–5. doi:10.1136/ip-2022-044580

Original research

Effect of a new concussion substitute rule on medical

assessment of head collision events in Premier

Leaguefootball

Gabriel Tarzi ,

Christopher Tarzi ,

Diana Mirsu,

Jay Patel,

Eileen Dadashi,

Jana El- Sabbagh,

Austin Gerhart,

Michael D Cusimano

1,2

To cite: TarziG, TarziC,

MirsuD, etal. Inj Prev Epub

ahead of print: [please

include Day Month Year].

doi:10.1136/ip-2022-044580

Injury Prevention Research

Ofﬁce, Division of Neurosurgery,

St Michael’s Hospital, Toronto,

Ontario, Canada

Division of Neurosurgery, St.

Michael’s Hospital, University

of Toronto, Toronto, Ontario,

Canada

Correspondence to

Dr Michael D Cusimano,

Department of Surgery, St.

Michael’s Hospital, University

of Toronto, Toronto, Canada;

injuryprevention@ smh. ca

Received 13 March 2022

Accepted 10 June 2022

employer(s)) 2022. Re- use

permitted under CC BY- NC. No

commercial re- use. See rights

and permissions. Published

by BMJ.

ABSTRACT

Objective To investigate the utilisation of additional

permanent concussion substitutes (APCSs) and its

efﬁcacy with regards to rate and duration of medical

assessment of head collision events (HCEs) in the

2020–2021 Premier League season. The present APCS

rule allows players with a suspected concussion to be

removed from a match without counting towards a

team’s allocated substitutions.

Methods Eighty Premier League matches, 40 prior

to additional permanent concussion substitutes

implementation (Pre- APCS) and 40 after (Post- APCS),

were randomly selected and analysed by a team of

trained reviewers for HCEs. Data on HCE incidence, rates

of medical assessment, duration of medical assessment

and return to play were collected for each match. Data

for the Pre- APCS and Post- APCS groups were compared

to analyse differences in assessment of HCEs.

Results During the 2020–2021 Premier League season,

three APCSs were used. There were 38 HCEs identiﬁed

in the Pre- APCS group (0.95 per match, 28.79 per 1000

athlete- hours of exposure) and 42 in the Post- APCS

group (1.05 per match, 31.82 per 1000 athlete- hours of

exposure). Incidence of HCEs (p=0.657), rates of medical

assessment (23.7% Pre- APCS vs 21.4% Post- APCS;

p=0.545) and duration of medical assessment (median

81 s Pre- APCS vs 102 s Post- APCS; p=0.466) did not

signiﬁcantly differ between the two groups.

Conclusions The implementation of APCSs in the

Premier League did not impact the rate or duration of

medical assessement of HCEs. Despite the introduction

of APCSs, the consensus protocols for HCE assessment

were rarely followed. We recommend changes to

APCS and its implementation that would be aimed at

protecting player health.

INTRODUCTION

Sport- related concussion (SRC), a subset of mild

traumatic brain injury, has been the subject of

increased research over the last decade. The current

internationally agreed on protocols for SRC assess-

ment states that players suspected of sustaining

a concussion should be removed from play and

assessed according to standardised tests by a licensed

healthcare provider.

Proper medical assessment for

athletes involved in head collision events (HCEs) is

necessary to prevent further neurological compli-

cations that are associated with premature return-

to- play.

1 2

Association football, otherwise known as foot-

ball or soccer, has one of the highest incidences of

concussion in sport.

Previous research has shown

that International Conference on Concussion

in Sport (ICCS) assessment protocols were not

followed for HCEs at four elite international foot-

ball tournaments, despite being organised by the

Fédération Internationale de Football Association

(FIFA), which has endorsed the ICCS protocols.

3–6

Further, research on medically diagnosed concus-

sions in the French Football Federation revealed

that over a quarter of concussed players were not

given sideline assessments and of those assessed,

over half were allowed to resume play.

One reason

why concussion protocols had not been imple-

mented widely in elite levels of football was that

substitution rules necessary for the proper assess-

ment of players were lacking in football. It was

argued that due to the limited number of substitu-

tions available, teams may have been hesitant to use

a substitution for injured players, or to allow for

WHAT IS ALREADY KNOWN ON THIS TOPIC

⇒ In elite football, head collision events (HCEs) are

rarely assessed in accordance with consensus

protocols and medical recommendations.

⇒ Introduction of the additional permanent

concussion substitute (APCS) rule in the Premier

League on a trial basis aims to protect player

health by allowing the removal of players

involved in HCEs without counting towards

a team’s allocated substitutions, thereby

encouraging medical assessment.

WHAT THIS STUDY ADDS

⇒ The introduction of the APCS rule did not

impact the rate or duration of medical

assessment of HCEs in Premier League football

and was only used three times throughout the

entire season.

⇒ The rate and duration of medical assessment of

HCEs are still not in accordance with consensus

protocols and medical recommendations,

despite the introduction of the APCS rule.

HOW THIS STUDY MIGHT AFFECT RESEARCH,

PRACTICE OR POLICY

⇒ The APCS rule did not serve its intended

purpose and the rules and protocols in football

will need to be revised to truly protect player

health.

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Original research

proper medical assessment, rather opting to use tactical player

substitutions instead.

In other professional sports, rule changes, such as the use of

independent medical observers in American football and concus-

sion substitutes in Australian rugby, have led to improved iden-

tification of SRCs.

8–11

Concussion- related protocol changes in

football have been rare; however, research has shown that these

ameliorations may decrease concussion incidence.

In December

2020, football’s rule- making governing body, the International

Football Association Board (IFAB), approved the use of addi-

tional permanent concussion substitutes (APCSs) to be used

on a trial basis. The substitutions could be made at any point

following an HCE, or as concussion symptoms developed, and

would not count towards the three regular substitutions to which

a team is entitled per match.

By not counting towards the allo-

cated substitutes available, an APCS removes potential tactical

disadvantages for teams and even allows for injured players to

be replaced regardless of the number of substitutions used prior.

However, a player that is removed through an APCS would be

unable to return to play for the remainder of the match.

In 2021, the English Premier League (PL), the most viewed,

followed and largest domestic football league in the world,

agreed to participate in the IFAB’s trial of APCSs.

‘Protocol

B’, which allows for two APCSs per team per game, was imple-

mented by the PL from Matchweek 23 until the end of the

2020–2021 season (Matchweek 38).

This trial rule has been a

long- awaited change for professional football players, who have

been campaigning for concussion substitutes since 2013.

16 17

Given the fact that APCSs have only been introduced on a trial

basis in select leagues, there is no existing literature on its effi-

cacy. The objective of this study is to investigate the utilisation

of APCSs in the PL and analyse how the implementation of the

APCS rule has impacted the rates and duration of medical assess-

ment of HCEs. The implementation of APCSs aims to protect

player health by providing team medical staff and coaches

with the ability to remove a player involved in an HCE from a

game and provide the necessary assessments without tactical or

numerical disadvantages. The introduction of APCSs in football

is novel and is currently only being employed on a trial basis.

With no existing research on the implementation of the APCS

rule in football, this research has implications for future deci-

sions on similar rule- changes regarding concussion substitutes

worldwide.

METHODS

Study sample

A total of 380 matches were played during the 2020–2021 PL

season between 12 September 2020 and 23 May 2021. A total of

220 PL matches (58%) were played prior to the implementation

of APCS and 160 PL matches (42%) were played after the imple-

mentation of APCS. A total of 80 PL matches, 40 matches prior

to APCS implementation (termed Pre- APCS) and 40 matches

after APCS implementation (termed Post- APCS), were randomly

selected using a random number generator and analysed by

trained reviewers for HCE data collection. The sample size was

calculated to detect a 25% increase in duration of assessment

between the Pre- APCS and Post- APCS groups. Using data from

prior published work, with identical definitions and method-

ology, we used an average duration of 59.9 s of assessment per

HCE, SD of 31.1 s and an average of 1.36 HCEs per match in

our calculation.

Given that prior work has shown increases in

assessment times of nearly 20 s, our sample size was designed to

be able to detect a 25% increase in assessment time with an alpha

of 0.05 and power of 0.80.

All players involved in PL matches

during the 2020–2021 season were eligible to be included in this

study. Patients and the public were not involved in this study.

HCE identiﬁcation and data collection

HCEs are defined as per prior research.

3–6

HCEs are incidents

in which a player suffers a direct head contact and as a result is

unable to resume play within 5 s. The term HCE encompasses

a wide range of head collisions which can potentially result

in a concussion and merit medical assessment. Events such as

intentional headers are not defined as HCEs unless the player

involved is unable to carry on with play. Ambiguous events, such

as clear embellishment, lacked conclusive video evidence of head

contact, or minor head contact (eg, fingers lightly brushing play-

er’s head) are excluded from the study.

Reviewers were trained per prior descriptions until reviewers

showed an inter- rater Kappa coefficient of 0.85 or higher.

Two independent reviewers carefully watched video footage

and collected information on the occurrence of HCEs per

match(table 1). Medical assessment was defined as any assess-

ment to an injured player conducted by team medical personnel.

The duration of medical assessment was defined as the time, in

seconds, between a player receiving assessment to them returning

to play or their removal from play, whichever occurred first. Any

discrepancies between the two reviewers analysing a match were

resolved by a third independent reviewer. The Cohen’s kappa

coefficient among reviewers was 0.87. Any HCEs that resulted

in the use of an APCS that were not captured in our study sample

were retrospectively identified and analysed as a descriptive

narrative.

Statistical analysis

Descriptive statistics was reported as frequencies, ratios or

medians. For comparison of median time of assessment, the

Mann- Whitney U test was used. To compare categorical variables,

the Fisher’s exact test or χ

was used as appropriate. Comparison

of incidence was estimated by quasi- Poisson generalised linear

models, assuming 90 min of exposure for 22 athletes per match.

Table 1 Variables collected by reviewers for analysis for each head

collision event (HCE) identiﬁed

Variable Description

No. players

involved

The number of players involved in the HCE, including the injured

player (numerical)

Medical

assessment

Whether the injured player received assessment from team medical

personnel (binary)

Assessment

location

The location where injured players were assessed by medical

personnel, includes: no assessment, on ﬁeld, on sidelines, elsewhere

in the stadium/hospital

Time assessed Time that injured player was assessed by medical personnel until

return to play in seconds (s)

Return to play Time until injured player returned to play, includes: immediately

following assessment on pitch, immediately following assessment on

sidelines, in the same half, removed from game, removed from game

via APCS

Score Score of the game in reference to the injured player’s team, includes;

tied, winning, losing

Foul Whether the referee determined there was a foul for the HCE (binary)

No. signs of

concussion

The number of signs of concussion demonstrated by the injured

player, includes: slow to get up, clutching of the head, disorientation/

daze, loss of consciousness, obvious disequilibrium

APCS, additional permanent concussion substitute.

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Original research

A significance level of 5% was used for all tests. SPSS1.0.0.1406

for macOS was used to conduct the analysis.

RESULTS

HCE identiﬁcation

Of the 80 sampled games in the 2020–2021 PL season, we iden-

tified 77 incidents of HCE. Three events involved two players

meeting the defined criteria for an HCE, resulting in a total of

80 HCEs in 80 sampled games. In the Pre- APCS group, 38 HCEs

were identified in 40 games (0.95 HCEs per match, 28.79 HCEs

per 1000 athlete- hours of exposure), in the Post- APCS group,

42 HCEs were identified in 40 games (1.05 HCEs per match,

31.82 HCEs per 1000 athlete- hours of exposure). Between the

two groups, there was no significant difference in the incidence

of HCEs (IRR: 0.9048, 95% CI (0.5677 to 1.4377), p=0.657)

(table 2).

HCE assessment

In the sample of matches analysed, there were no APCSs used.

There was no difference in the rate of medical assessments

before or after the rule change (9/38 (23.7%) Pre- APCS vs 9/42

(21.4%) Post- APCS) (p=0.545). The location of assessment, that

is, on- field or sideline, was not significantly different between

Pre- APCS and Post- APCS groups (p=0.540). After medical

assessment, the time until return to play was also not signifi-

cantly different after the implementation of APCS (p=0.641)

(table 2).

For players that were medically assessed, the median duration

of assessment by team medical personnel was 81 s and 102 s for

the Pre- APCS and Post- APCS groups, respectively (p=0.466). In

our analysis, no players were removed from the game following

an HCE in the Pre- APCS group and no APCSs were used in the

Post- APCS group.

HCE characteristics

The score of the game at the time of the HCE, in reference to

the injured player’s team, in terms of winning, losing or tying,

was not significantly different between the Pre- APCS and Post-

APCS groups (p=0.122). The assessment of fouls for HCEs by

referees was also not significantly different between the Pre-

APCS and Post- APCS groups (p=0.541). The number of signs of

concussions displayed by a player involved in an HCE between

the two groups was not significantly different (p=0.653). For

HCEs that resulted in the injured player displaying more than

one sign of concussions, there was no significant difference in

the rate of medical assessment between the Pre- APCS and Post-

APCS groups (p=0.798). When comparing the rates of medical

assessment for HCEs resulting from head- to- head contact, which

has been shown to be the most high- risk mechanism of injury,

between groups, there was no significant difference (p=0.545)

(table 2).

Utilisation of APCS

In the 2020–2021 PL season, there were three reported occa-

sions in the 160 matches played after the rule implementation

that APCSs were used to remove a player involved in an HCE

from a match. In all three occasions, the player that was involved

in the HCE was sliding/tackling to take possession of the ball.

Two of the HCEs were a result of knee- to- head contact with

another player and one as a result of head- to- field contact. Two

of the injured players showed three signs of concussion and one

showed four signs of concussion. The respective times of medical

assessment were 180 s, 900 s and 180 s. In one incident, the

player involved in the HCE was cleared by medical staff to play

before an APCS was used approximately 10 min later. A break-

down of each event is summarised in table 3.

DISCUSSION

In the 80 PL games analysed before and after the APCS rule

change, we found no significant differences in the incidence,

rates of medical assessment or duration of medical assessments

for HCEs between the groups. Both the Pre- APCS and Post-

APCS groups had lower rates of medical assessment of HCEs

compared with other elite football tournaments, such as the

World Cup and European Championship.

3–6

Both groups had

greater duration of medical assessment of HCEs than those elite

tournaments.

However, the duration of medical assessment of

HCEs in the PL is still considerably shorter than the estimated

10 min required to complete a proper Sport Concussion Assess-

ment Tool.

Despite the APCS rule, the rates and duration of

medical assessments of HCEs in the PL still do not adhere to

the consensus protocols for concussion assessment supported by

FIFA. The aims of the APCS rule become obsolete if players are

not being properly assessed immediately after an HCE.

In the 2020–2021 PL season, there were only three instances

when the APCS was used by teams. In two of the cases, the players

involved in an HCE were removed from the match immediately,

and in the third case, the player continued play before eventually

being removed from the match. In one case, the injured player’s

team had already used their allocated substitutions before the

HCE, meaning the APCS allowed for the removal of an injured

player that would not have been available before the rule change.

Limitations of APCS

The lack of effect of APCS can potentially be explained by several

factors. First, the rule change was implemented mid- season and

Table 2 Head collision event (HCE) outcomes and assessment before and after additional permanent concussion substitute (APCS) implementation

in the Premier League

Outcome Pre- APCS (n=38) Post- APCS (n=42) Signiﬁcance

HCEs per 1000 athlete- hours of exposure (95% CI) 28.79 (20.37 to 39.51) 31.82 (22.93 to 43.01) p=0.657

IDR=0.9048 (0.5677, 1.4377)

Medically assessed, No. (%) 9 (23.7) 9 (21.4) p=0.545

Duration of medical assessment, median (IQR), s 81 (50) 102 (213) p=0.466

No. signs of concussion

1 2 2 p=0.653

2 36 40

≥3 0 0

Foul assessed, No. (%) 15 (39.5) 16 (38.1) p=0.541

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Original research

so, the late introduction may not have provided medical staff

and players alike the necessary time to understand APCS’s role

in the game. The utilisation of APCSs requires all stakeholders to

understand their role in protecting player health. Referees play a

key role as they can stop play for medical assessment and allow

medical staff to enter the pitch. Team medical staff are respon-

sible for assessing players, but as employees of the team they

must relay information to the coach who ultimately makes the

decision on substitution. Future research should investigate the

long- term impacts of the APCS rule on medical assessments if it

is implemented permanently. We chose to focus on the 2020–21

PL season because it allowed for comparison of similar groups

(same teams, coaches, players and referees) and given it is a trial-

based rule change we felt it important to analyse it in a timely

manner before a final decision was made.

In addition, the matches in the Post- APCS group were played

in the latter half of the season when matches may hold greater

significance with regards to final league standings, potentially

making an APCS undesirable as coaches may not want to remove

starting players. In our perspective, a drawback of APCS is that

it demands that teams make a permanent substitution for the

player being assessed. Injured players who are assessed and

deemed cleared to play after the necessary medical assessments

are completed may not to return to play. This weakness in APCS

likely discourages its usage. Lastly, APCSs may not influence

rates of medical assessment of HCEs because teams may only

use APCSs in the most severe and obvious cases of head injuries,

more subtle events that require more in- depth medical assess-

ment may not meet the threshold teams may have for permanent

substitution, particularly if the player is permanently removed

from the game. Teams may thus not want to risk the outcome

of a game by removing players for what they see as more minor

HCEs. ICCS protocols indicate that every HCE should be

medically assessed regardless the number of signs of concus-

sion displayed or perceived severity.

So that every player can

be properly assessed after an HCE, we propose policy recom-

mendations for the APCS rule that can help mitigate the present

limitations of APCS and potentially improve player safety.

Policy recommendations

The world players’ union, FIFAPro, has long called for tempo-

rary concussion substitutes and has voiced its concerns with the

current rules surrounding APCSs.

17 20

And unlike rule- changes

aimed at removing potentially concussed players from play in

other professional sport leagues (eg, National Football League),

which can be ordered by independent medical observers, the

decision regarding removal from an APCS still relies on team

coaches who may have motivations other than player health.

Experience from other professional sports leagues highlights

several potential avenues to improve the APCS rule in football by

adapting temporary substitutions, mandatory assessment proto-

cols and independent medical observers. The National Rugby

League (NRL) in Australia introduced a similar rule to the APCS

called the Concussion Interchange Rule (CIR). The CIR allows

for players who are cleared after medical assessment to return

to play and was heavily used, with a total of 167 concussion

interchanges in one season.

This may be largely in part because

the CIR allows for players to return to play after assessment

(ie, temporary substitution if cleared by medical staff), which

more than half the players who were removed through the CIR

did.

Studies conducted in American football show that the use

of independent medical observers to remove players involved

in HCEs significantly increased the likelihood of a concussion

diagnosis, supporting their effectiveness.

Similar to NRL rules,

World Rugby has long implemented a Head Injury Assessment

(HIA) rule which outlines a series of on and off- field checks

conducted by independent match- day doctors that players

must undergo after a head injury, including video review.

The

HIA rule has been shown to be effective at identifying concus-

sion with removal- from- play decisions having good specificity

for concussion diagnosis.

The availability of Video Assistant

Referee (VAR) in football creates the opportunity for indepen-

dent medical observers in football to review footage of HCEs

that is not visible to the on- field referee and medical staff. VAR

would allow for medical observers to be in direct contact with

the on- field referee and notify them when play needs to be

stopped for assessment. In addition to this, the PL should intro-

duce mandatory concussion awareness training and education

for all owners, boards of directors, players, coaches, medical

staff and referees. Teams should also be mandated to raise aware-

ness on concussion prevention in their communities, given their

influence on younger players and fans. More accountability

should be placed on referees as they are the only individuals that

can stop play for assessment and enforce rules. Lastly, to further

discourage competitive factors from influencing APCS decisions,

we recommend sanctions to teams that do not follow established

procedures in player health. Sanctions could range from mone-

tary fines to point deductions in league standings to teams whose

on- pitch actions do not prioritise player health. Ultimately, lead-

ership from the PL, FIFA and the IFAB will be required to amend

the APCS rule to increase its usage and subsequently improve

player health.

Limitations

This study relies on the analysis of video footage, where the

reviewers cannot control camera angles/movement resulting in

potentially missing off- camera HCEs and of the exact duration

of medical assessments. In addition, on- field audio information,

which could have informed the type of medical assessment or

the decision- making process, was not available to reviewers.

Finally, our random sample of 80 PL matches did not capture the

three instances where APCSs were used, but the circumstances

surrounding these events were reviewed.

Conclusion

Introduction of a concussion substitute rule into PL football for

players involved in an HCE was not associated with any change

in the occurrence of HCEs, the rate of medical assessment or

the duration of medical assessments of HCEs. In spite of the

Table 3 Description of additional permanent concussion substitutes (APCSs) used in the 2020–2021 Premier League season

Event no.

No. players

involved

Position of

injured player

Action of player

before injury

Mechanism of

injury

Time of medical

assessment (s)

No. signs of

concussion Return to play following assessment

1 2 Defender Sliding/tackling Knee- to- head 186 3 Immediately removed from play

2 2 Goalkeeper Sliding/tackling Knee- to- head 900 4 Immediately removed from play

3 2 Defender Sliding/tackling Head- to- ﬁeld 180 3 Returned to play before removal

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Original research

rule change, medical assessments for HCEs as outlined in ICCS

protocols were rarely followed. Changes to the APCS rule in

football, such as those we have recommended, will be required

before it can possibly aim to improve and protect player health.

Contributors The corresponding author attests that all listed authors meet

authorship criteria and that no others meeting the criteria have been omitted.

MDC is the guarantor and had full access to all of the data in the study and takes

responsibility for the integrity of the data and the accuracy of the data analysis. GT,

MDC contributed to concept and design. GT, CT, DM, JP, ED, JE- S, AG contributed

to acquisition, analysis or interpretation of data. GT, CT, DM contributed to drafting

of the manuscript. CT, DM, JP, ED, JE- S, AG, MDC contributed to critical revision of

the manuscript for important intellectual content. GT, CT contributed to statistical

analysis. MDC contributed to supervision.

Funding This work was supported by the Canadian Institutes of Health Research

Strategic Team Grant in Applied Injury Research TIR- 103946.

Competing interests None declared.

Patient and public involvement Patients and/or the public were not involved in

the design, or conduct, or reporting, or dissemination plans of this research.

Patient consent for publication Not applicable.

Ethics approval The Research Ethics Board at St. Michael’s Hospital waived the

need for ethics approval.

Provenance and peer review Not commissioned; externally peer reviewed.

Data availability statement Data are available upon reasonable request.

Open access This is an open access article distributed in accordance with the

Creative Commons Attribution Non Commercial (CC BY- NC 4.0) license, which

permits others to distribute, remix, adapt, build upon this work non- commercially,

and license their derivative works on different terms, provided the original work is

properly cited, appropriate credit is given, any changes made indicated, and the use

is non- commercial. See:http://creativecommons.org/licenses/by-nc/4.0/.

ORCID iDs

GabrielTarzi http://orcid.org/0000-0002-1497-2359

ChristopherTarzi http://orcid.org/0000-0003-0809-8391

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