Soccer is the most popular team sport in Switzerland [1]. Amongst the 15- to 74-year-old population, about 480,000 persons play soccer, which corresponds to a percentage of 7.8% of this population [2]. Of these, 190,000 individuals participate in official championships. According to international studies, the overall injury incidence for competitive amateur soccer players ranges from 5.2 to 9.6 per 1000 hours of play [3-5]. Prior research has compared incidence rates in amateur and professional soccer, yielding inconsistent findings. While van Beijsterveldt et al. [6] compared an amateur cohort to a professional one and found a higher injury incidence in amateur soccer players including an increased risk for moderate and severe injuries, other studies reported a lower [7] or comparable [8] injury risk for specific amateur soccer populations compared with professional players. Given the high number of players involved in amateur soccer and the high injury risk, it is perhaps surprising that only a few investigations have provided information about the circumstances leading to injuries in this setting. For instance, previous studies have shown that - as in professional soccer - player to player contact is a frequent injury mechanism in amateur soccer games, causing more than half of all injuries [4, 9]. In training however, non-contact injuries seem to be more common than injuries due to player contact. Interestingly, the frequency of contact injuries does not vary between high- and low-level players when only severe injuries are considered [10].

With regard to the contributing factors which lead to injuries in amateur soccer, contact with another player is the most frequent injury mechanism followed by distortion and turning/twisting [5]. Moreover, in their review on incidence and prevention of soccer injuries Junge and Dvorak [11] found that 12% to 28% of all injuries were caused by foul play. However, this review was not exclusively focussed on amateur soccer. These data accord well with another investigation with players of different skill levels, in which almost 30% of traumatic injuries were associated with foul play [12].

Despite these findings, it should be noted that amateur soccer is not a homogenous setting. Only a few studies have factored in various levels of amateur soccer, and these have found contradicting results. Peterson et al. [12] compared players from all levels (including top level) and concluded that while low-level players had lower exposure to soccer, they were more likely to get injured. In contrast, Schmikli et al. [13] identified more skilled adult amateur players as a target group for prevention, because they had an increased injury risk. Hammes et al. [8] exclusively focussed on veterans (aged 32 or older) who played competitively in a separate league. They found an injury incidence that was comparable to other male soccer levels, but injury characteristics were different. In summary, these finding clearly underline the importance of research within different amateur soccer populations.

Finally, besides competitive amateur soccer, a high number of people play soccer non-organised. Of the 15- to 74-year-old Swiss population, 290,000 persons practice soccer outside of clubs and official championships [2]. To the best of our knowledge, no studies exist so far with regard to the epidemiology of soccer injuries in non-organised settings. Taken together, we suggest that there is a lack of data regarding soccer accidents in specific non-professional soccer populations. Therefore, the aim of the present study was to analyse and compare incidence, causes and characteristics of injuries in different settings of organised and non-organised non-professional soccer.

Of the 705 reported injuries, 48.9% (n=345) happened during organised soccer games, 21.0% (n=148) during organised soccer training, and 30.1% (n=212) during non-organised soccer play. Out of the injuries which occurred during non-organised soccer, 61.3% (n=130) occurred while playing with family or friends, 19.3% (n=41) during fun tournaments, 7.5% (n=16) in other sport clubs, 4.2% (n=9) at school, 3.3% (n=7) in alternative leagues, and 4.2% (n=9) in other settings. Whether or not a soccer accident happened in an organised or non-organised context was not associated with the severity of the injury (p>0.05). The distribution of injury setting by gender and age is shown in Table 1. Participants who were injured during a game were on average 26.3 (SD=9.2) years old and somewhat younger than participants who were injured during training (M=29.0, SD=10.9, p=0.008) or during non-organised soccer (M=30.5, SD=11.7, p<0.001). 6.1% (n=43) of the injuries affected a female player. No significant gender differences were found with respect to the three main injury settings (p>0.05). Unlike injury type (p>0.05), injury location was influenced by the setting (p=0.007). In particular, differences were identified concerning knee injuries (p=0.032), head injuries (p=0.010), and thigh and upper leg injuries (p=0.019). While a higher percentage of knee injuries was identified during games (28.1%) compared to non-organised soccer play (18.4%, p=0.010), the number of knee injuries in training (26.4%) did not significantly differ from the other settings (p>0.05). Additionally, there was a higher percentage of head injuries in games (9.0%) than in non-organised soccer (2.8%, p=0.005), but again no difference was found with respect to training (4.7%, p>0.05). Injuries to the thigh and upper leg occurred more frequently in non-organised soccer (7.1%) than in games (2.3%, p=0.006).

As shown in Table 2, a significantly higher proportion of contact injuries and foul play injuries (subjective appraisal) were identified in games compared to training (p<0.001) or non-organised soccer (p<0.001). Additionally, in games, every fourth injury (27.4%) was caused by a foul play penalised by the referee. When considering game injuries only, there were no significant differences in the proportion of contact injuries between different amateur soccer leagues (p>0.05). However, the number of foul play injuries differed significantly between leagues (subjective appraisal: p=0.031, penalised by the referee: p=0.033). A particularly high foul play rate was found in the 30+ leagues. Focussing on non-organised soccer settings only (playing with family or friends, fun tournaments), no significant difference with respect to contact and foul play injuries was identified (p>0.05).

With regard to injury situations, being tackled by an opponent (16.3%, n=115), collisions (14.5%, n=102), other contact situations (10.4%, n=73), twisting and turning (8.1%, n=57), heading and aerial duels (7.7%, n=54), and running (7.2%, n=51) were the most frequently reported situations leading to an injury. As presented in Fig. (1), the most obvious difference with respect to the injury situation appears between games and non-organised soccer. Compared to training and non-organised soccer, in games, more injuries were caused by tacklings by an opponent (training: p=0.001; non-organised soccer: p=0.015) and heading or aerial duels (training: p=0.005; non-organised soccer: p<0.001). While collisions (p=0.004) and other contact injuries (p=0.012) happened more frequently in games than in non-organised soccer, running was a more frequent cause of injury during non-organised soccer play (p<0.001).

The comparison of different groups of amateur leagues yielded significant differences regarding preventive behaviour (Table 3). Players of the 1st-3rd amateur leagues attached more importance to core strength training than players of any other level (p≤0.001), except for women’s leagues (p=0.017). Additionally, players of 30+/40+ leagues stated less frequently that they had performed a core strength training prior to the injury compared to 4th-5th amateur league players (p=0.001). Less than half of all 30+/40+ leagues players had performed a general strength training.

Fig. (1). Percentages and 95% confidence intervals of situations leading to an injury, separately for different soccer settings (n=705).

In soccer club members, the estimated injury incidence was 10.7 (95%-CI 9.7-11.9) per 1000 hours of soccer play. The injury incidence was highest for 30+/40+ league players with 18.7 injuries per 1000 hours exposure and differed significantly from other males (1st-3rd amateur leagues: p=0.002, 4th-5th amateur leagues: p=0.007), female (p=0.006) and junior (p<0.001) leagues, except for other leagues (p>0.05).

The major outcome of this study is that substantial differences exist between various non-professional soccer settings with respect to injury characteristics, causes and incidence. A particularly high incidence rate was found among 30+/40+ league players.

For organised soccer players, an incidence rate of 10.7 injuries per 1000 hours of soccer participation was calculated. Even though other studies in amateur [4, 6] and professional [16, 17] soccer found similar or somewhat lower injury rates, a direct comparison of the results is difficult as the present study only included participants who had sustained at least one injury. This may have led to an above average proportion of injury-prone persons and thus an increased injury incidence.

Nevertheless, the presented comparisons between the injury incidences of different amateur soccer leagues should be reliable. Players of 30+/40+ leagues were identified as high-risk group having an increased injury incidence of 18.7 injuries per 1000 hours of play. Based on the fact that players of 30+/40+ leagues had a relatively low exposure time of 2.8 hours per week, it can be assumed that they mainly play in a competitive setting and practice soccer up to once per week. Generally, an increased injury risk in games of veteran soccer players has been reported previously [7], which together with the low training to game ratio leads to an increased overall injury incidence [8]. Hammes et al. [8] calculated a somewhat lower injury incidence of 12.4 injuries per 1000 hours of soccer, because they only included veteran teams (players aged 32 years and older) that performed weekly training sessions, which led to a higher training to game ratio of 2:1. Of particular interest in this context is that players of 30+/40+ leagues reported less frequently that they participated in injury prevention measures compared to players of other leagues. Compared with other levels, physical conditioning is less frequently part of the training sessions in veteran soccer [18]. Thus, adjusted prevention strategies for 30+/40+ league players seem warranted to reduce the high injury risk in this particular group [19].

While injury severity and injury type did not differ between settings (games, training, non-organised soccer), a higher percentage of knee injuries was identified in games compared to non-organised soccer. Considering the fact that knee injuries are predominantly caused without contact¹², this difference could be explained by the less competitive character of the game in non-organised soccer which leads to a lower speed and slower changes of direction. Focussing on medical attention injuries in organised amateur soccer, Herrero et al. [7] reported a percentage of knee injuries (29.9%) comparable to our study, whereas Schmikli et al. [13] registered a lower percentage (19.3%), most likely because less severe injuries were also included in their study. Other investigations yielded comparable percentages of knee injuries in amateur soccer (between 15.1% and 24.3%) [6, 9, 20].

Injuries that resulted from contact with an opponent occurred more frequently during games than during training [20] or non-organised playing, which corroborates a higher level of physical play in games of amateur soccer [21]. This leads to a high proportion (41.2%) of injuries caused by foul play in this setting. In our study, more than one quarter of injuries during amateur soccer games happened due to foul play, if the referee’s decision was taken into account. This result is in line with other studies carried out in amateur soccer²⁰ and different levels of professional soccer [11].

Moreover, little is known so far about injury situations in amateur soccer. The present study points out that injuries caused by tackling of an opponent happen more than twice as frequently during games as during training [15], while injuries caused by collisions and other contact situations (pushing, duel without clear ball possession, etc.) occur with a comparable frequency. Injuries caused by heading and aerial duels represent an explicit problem of competitive amateur soccer. Injury situations involving contact with an opponent were significantly less frequent in non-organised soccer. By contrast, a higher amount of injuries were self-inflicted, for example, while running. In summary, although the present study provides preliminary insights regarding the underlying injury mechanisms, more research is needed to gain a more complete understanding of the most relevant factors leading to injuries in different soccer settings and across amateur soccer levels.

This study clearly highlights the need for attractive and specific prevention programs addressing players of 30+ and 40+ amateur soccer leagues. Generally, differences in injury causes and characteristics by setting indicate that a more targeted approach of injury prevention is needed. Furthermore, playing competitive amateur soccer involves a higher risk of contact and foul play injuries compared to amateur soccer training or non-organised soccer. Therefore, players, coaches, referees and club officials in amateur soccer need to be more involved in fair play measures to promote a cooperative play.