The frequency of head injuries in professional football (soccer) is rather low compared with other contact or collision sports such as American football, rugby, or ice hockey.1–6 Head traumas in football typically occur because of body or object contact such as goal posts, balls, or the ground.5,6 Head traumas such as sport-related concussions may cause long-lasting impairment.7–9 Potentially, repetitive head traumas may be a risk factor for an impairment of long-term brain health.10,11
To prevent head injuries, it is necessary to know typical circumstances of such incidents: the players' actions on the pitch immediately preceding the head injury, and the ball possession status seem to be important aspects in this regard.12,13 For this purpose, video analysis is a useful technique.5,6,12,14–18 Fuller et al6,19 investigated injury mechanisms leading to head and neck injuries in international tournaments through this technique. They identified clash of heads and furthermore elbow to head strikes as the main cause of head injuries. As a consequence, the International Football Association Board (IFAB) enforced a rule change in 2006: Intentional elbow to head strikes had subsequently to be penalized with a red card. The influence of this rule change on head injuries has not yet been investigated.
The primary purpose of this study was to describe and assess circumstances immediately preceding head injuries in professional male football. A secondary aim was to investigate whether the rule change affected these circumstances. The analysis of various head injury types and their distinct injury mechanism are published elsewhere.20
Study Sample and Design
A retrospective analysis of head injuries in the first male German Bundesliga was completed encompassing the seasons 2000/2001 to 2012/2013. There are 18 teams in the league with a mean of 570 active players in total per season. The rule change (red card in case of intentional elbow to head strikes) was introduced at the beginning of the season 2006/2007, which was excluded from statistical analysis to guarantee an even distribution of seasons before and after the rule change and to allow for accustomization of players and referees to the new rule. This season was thus seen as a transition season. No Research Ethics Board approval was required for this study because all data were collected from public sources.21
At first, head injuries were identified by a structured search in the German football magazine “kicker Sportmagazin,” which is published twice weekly with 1 journalist being responsible for 1 club and having contact with the club every day. The magazine presents injury reports. In addition, a free-text search with defined search terms was conducted. It provided all relevant data on diagnosis such as concussions/traumatic brain injuries, contusions, facial fractures, and lacerations/abrasions. The diagnoses were forwarded by team officials. Afterward, video sequences of these head injuries were obtained from the official German Football League [“Die Liga—Fußballverband (DFL)”]. Circumstances leading to head impacts and subsequently head injuries were analyzed from those video recordings.6,12,21
The observational criteria of head impacts during matches are listed below.6,12,18,19 In case, a head injury involved a player–player contact, the second player is referred to as the “non-injured player.” A “free ball” situation means 2 players challenge for the ball at the same time. “Player's ball possession” implies that 1 player is clearly in possession of the ball. Head injuries without video recordings are excluded in the analyses referring to total numbers and percentages.
- Action performed by the noninjured player: heads the ball, 1/2 footed tackle, slides in, raises elbow, pushes injured player, runs into injured player, runs (forwards, backwards, and sideways), falls on the injured player, jumps (sideways, forwards, backwards, and upwards), and stands.
- Action performed by the injured player: heads the ball, 1/2 footed tackle, slides in, raises elbow, pushes opponent, runs into opponent/team mate, runs (forwards, backwards, and sideways), runs against goal/corner flag/advertising boards, falls on the noninjured player, falls on the ground, jumps (sideways, forwards, backwards, and upwards), and stands.
- Foul—referee decision: yes, no card, yellow card, red card, and no.
- Foul—assessment of rater (football-experienced sports scientist): yes, no card, yellow card, red card, and no.
- Injured player aware of imminent impact: yes, no.
- Ball possession status at the time of the incident: injured player in ball possession, noninjured player in ball possession, and free ball.
- Bleeding as consequences of the head impact: yes, no.
- On-pitch treatment—first aid: yes, no.
Match exposure was recorded using the following calculation22: number of games × number of players on the field × duration of the game in hours (1.5 hours per match). This analysis included 34 games per team in the regular season plus games in official national and international competitions, for example, UEFA Champions-League or national DFB-Cup (DFB-Pokal). Extra time in knock out games (2 × 15 minutes) was also enclosed.
All statistical analyses were performed with Windows Excel 2010. The incidence rate (IR) for total head injuries was calculated with the following formula: incidence = (number of injuries/hours of match exposure) × 1000. For the IRs, 95% confidence intervals (CIs) were calculated23:
Chi-square analyses were performed to determine differences between the 2 periods. Descriptive data are presented as absolute numbers with percentages in parentheses. The significance level was set at P < 0.05.
This study includes 334 head injuries (196 head injuries during 2000/2001-2005/2006 and 138 during 2007/2008-2012/2013) corresponding to an IR of 2.25 (95% CI, 2.02-2.51) per 1000 player match hours. Of these 334 head injuries, 21% (n = 69) could not be analyzed in detail as either the video recordings were unavailable (17.5%, n = 58) or, despite the video recordings being present, the injury mechanism was not apparent (3.5%, n = 11). For the first period (2000/2001-2005/2006), 48 head injuries (25%) could not be analyzed and for the second period (2007/2008-2012/2013), 21 (15%).
The total football exposure for all 12 seasons was 148 269 player match hours and 74 519.5 player match hours for the seasons 2000/2001 to 2005/2006 and 73 749.5 for 2007/2008 to 2012/2013.
Tables 1 and 2 display the results of the video analysis. The 3 most frequent actions performed by the noninjured players at the time of the injury were jumping (sideways, backwards, forwards, and upwards) (64%), heading the ball (27%), or raising the elbow to the head (23%). The injured player predominantly jumped (sideways, backwards, forwards, and upwards) (60%), headed the ball (36%), or ran forwards (20%). No head injury of this study occurred after solely heading the ball in the light of purposeful heading with no contact with an opponent. Between seasons 2000/2001 to 2005/2006 and 2007/2008 to 2012/2013, the action “raising the elbow to head” was reduced by 23%. However, there was no large difference for either the injured or the noninjured player, if the 3 most frequent actions were compared. Seventy one percent of the injured players were aware of the imminent contact with either a player or an object.
Foul Play—Referee's Decision and Assessment of Rater
The referee rated 74% of the head injuries as no foul play. The foul assessment of the rater (football-experienced sports scientist) resulted in 62% in a no foul decision. The referee rated 26% of the head injuries as foul play and the rater 38%. In 7%, the referee showed the yellow card, the rater would have performed it in 24%.
Ball Possession, On-Pitch Medical Treatment, and Consequences of Head Impact
Eighty-one percent of the head injuries occurred during a free ball situation. On-pitch treatment was applied in 88%, 12% were untreated. Bleeding occurred in 54% of the head injuries.
Many studies in professional football have used video recordings to analyze injury mechanisms and their risk factors.12,14–18 However, only few research groups investigated head injuries specifically and these studies were conducted more than a decade ago.5,6,19 Considering the rapidly changing nature of football concerning speed, techniques, equipment, and game play in general (eg, tactics),24 a re-evaluation of factors promoting head injuries is important. Most players who suffered from a head injury were aware of the imminent contact with either an object or another player. This aspect is essential, as it allows the anticipation of the impact and subsequently offers the opportunity to react accordingly, to reduce the force of the impact and thus the severity of head injuries.
In this study, jumping for the ball was the most frequently performed action by the injured as well as by the noninjured players at the time of the head injury. This is in line with Fuller et al's findings.6 Especially free ball situations, when 2 players challenge for the ball in the air, had a greater propensity for injury in this study. The main aim of jumping is heading the ball. However, the ball as such does not seem to be a main risk factor for head traumas in professional football. Only 26% of the head injuries involved contact with the ball. No head injury of this study occurred after solely heading the ball, supporting this finding. This is also in accordance with the results of Fuller et al.6 They reported a low IR of 0.05/1000 football hours for head injuries because of solely heading the ball. Therefore, heading as such seems to be a rather low-risk activity in the light of traumatic head injuries. However, these results do not allow conclusions about the risk of gradual onset or chronic head injuries. Body contact either with the opponent or sometimes with the team mate is the main risk factor for head injuries. Previously published studies reported that especially elbow to head mechanisms were responsible. They caused up to 35% of all head injuries.2,5,6 As a consequence, the IFAB introduced a new rule in 2006 punishing conscious elbow to head movements with a red card. In the current study, a raised elbow to head by the noninjured player accounted for 23% of all head injuries. The number seemed to be lower by 23% after the rule change. It remains unknown how much the missing video recordings would have changed the players' action elbow–head contact.
Ball Possession and Foul Decision
The ball possession of the injured player has previously been discussed as risk factor having the greatest impact on the incidence of head injuries in football.6
Most injuries occurred after a free ball. Three-fourths of the duels were assessed as fair play and compliant with the current laws of the game by the referee. Most head to head contacts occurred therefore accidentally. Only 31% of all head injuries that occurred because of elbow to head contacts were assessed as foul plays. This emphasizes that in most duels an intentional strike with a part of the upper extremity, for example, the elbow, has not been the predominant action used by the noninjured player. Nevertheless, the raters assessed foul plays more frequently than the referees and decided to punish foul plays more often with a yellow card. But, no difference was found for red card decisions. Furthermore, there were no more red cards after the rule change in 2006. Low red card decisions were also found in a recent study with stricter interpretation of the rules over 1 season.25 It seems that it is rather difficult for referees to recognize foul plays appropriately.25
The remaining foul plays involved contact with a lower extremity, for example, a raised leg/foot. A rule penalizing “dangerous play” already exists. Nevertheless, punishing elbow strikes was a logical step following on from Fuller et al's6 and Andersen et al's5 results whose numbers were considerably higher compared with the results in this study. Reasons for this development may be the rule change in the first place. Less foul plays, an increase in fair play “thoughts” during header duels or an improved players' athletic performance allowing for higher jumps without the momentum's support by using the upper extremities might also explain this change.
Aware of Imminent Contact
Most players were most likely aware of an imminent impact. Being aware of the imminent contact is essential because it allows for the anticipation of the situation. The latter can reduce the injury risk as the player could, for example, activate his neck muscles to reduce head acceleration or he could try to move his head out of reach.26 Low head–neck muscle mass with reduced muscle strength was previously discussed as being a risk factor for high head accelerations in football with a subsequent high risk of head injuries.27 Thus, specific strength training for shoulder and neck musculature, teaching heading skills, improving peripheral vision, and reaction time may be recommended to prevent head injuries, although more data are needed to confirm and quantify efficacy. In addition, improving core and leg strength may help to maintain a stable position in the air during headers.
The head injuries were identified by a structured search in the football magazine “kicker Sportmagazin,” which is published twice weekly with 1 journalist being responsible for 1 club. This man power and expertise should allow for a decent accuracy of data.
The retrospective approach through an online open-source sports database has been previously used to gather information on injuries in professional football.28 Ideally, the video recordings should provide various perspectives, slow motions, and display a good quality. These prerequisites were not always met, for example, some injuries could be evaluated by 1 perspective only. Furthermore, 21% of the head injuries were not available on video recordings (eg, international games were completely missing or the injury was not caught on camera). The evaluation of on-pitch treatment, bleedings and referees' foul decisions require longer video sequences. Some sequences were stopped immediately after the head injury occurred making the assessment of those criteria impossible. Incidence rates and IR ratios were not calculated for the observational categories, as the large missing numbers of video sequences would have underestimated these rates. Unfortunately, the present data may be confounded by the relative number of missing data values. In addition, missing data were different between the 2 periods impairing the comparisons of observational criteria. Nevertheless, in this analysis, 21% of the head injuries were not completely available on video recordings. This percentage is in accordance with a previous study in which 20% were not identified.18 Other video analysis–based studies could not identify about 34%6 and 35%.5
As this analysis was based on retrospective data, the assessment of variables (eg, team habits, playing tactics, etc.), that may have contributed to injury risk, was not feasible. Furthermore, potential confounding factors such as age, height, weight, experience, player's position, or previous injury could not be obtained.
The present data suggest that jumping with the intention of heading the ball is the predominant players' action leading to a head injury. The rule change in 2006 led potentially to a reduction of “raising the elbow to head” movements that were deemed responsible for head injuries in many cases. Free balls caused by far the most head injuries as compared to being in ball possession. Using high-quality video material in future may help to keep identifying head injury prone match situations to develop preventative means.
The authors thank the “kicker Sportmagazin” magazine for granting access to their online issues. The video recordings were obtained from the official German Football League [“Die Liga—Fußballverband (DFL)”].
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