Fouls and yellow cards in the UEFA Champions League 2017-18

Purpose: In soccer, the fouls and cards showed by referees during a match represent aggressive behaviors of the players. This study aims to analyze the distributions of fouls committed by players in the 2017-18 UEFA Champions League, comparing positional roles in both home and away games. Methods: Fouls and yellow cards in matches of the qualification phase of the 2017-18 UEFA Champions League were collected from the UEFA website, and then recorded in a spreadsheet for analysis. Data from 32 teams and 599 outfield players were collected. Fouls per hour (FH) and yellow cards per hour (YCH) were calculated and used for the subsequent analyses. Results: Mean + standard deviation fouls and yellow cards per hour of play were 0.79 + 0.67 and 0.12 + 0.83 respectively. The comparison between positions showed a trend towards a significant difference between defenders and midfielders (0.70 + 0.55 and 0.86 + 0.72 respectively, p=0.051) for FH, and significant differences (p<0.01) for YCH between defenders (0.11 + 0.24), and attackers (0.04 + 0.14) and between midfielders (0.18 + 0.38) and attackers (0.08 + 0.14). A significant difference for FH between defenders (0.70 + 0.55) and midfielders (0.86 + 0.70) was observed in away games (p=0.013). Conclusions: The present findings show a higher foul rate in midfielders than attackers and defenders in UEFA Champions League games. On the contrary, defenders received more yellow cards than midfielders and attackers. These results can be explained by the greater distance covered by midfielders in comparison with the other positions and by tactical circumstances. Concerning yellow cards, it can be argued that defenders tend to commit fouls especially in situations that could lead the opposing team to score. The lower rate of fouls committed by defenders of away teams reflects previous studies, reporting a referee bias in favor of the home team.