The Twelfth Man? Refereeing Bias in English and German Soccer

This paper investigates potential bias in awards of player disciplinary sanctions, in the form of cautions (yellow cards) and dismissals (red cards) by referees in the English Premier League and the Bundesliga. Previous studies of behaviour of soccer referees have not adequately incorporated within-game information. Descriptive statistics from our samples clearly show that home teams receive fewer yellow and red cards than away teams. But biases may be wrongly identified where the modeller has failed to include within-game events such as goals scored and recent cards issued. What appears as referee favouritism may actually be excessive and illegal aggressive behaviour by players in teams that are behind in score. We deal with these issues using a minute-by-minute bivariate probit analysis of yellow and red cards issued in games over six seasons in the two leagues. The significance of a variable to denote score difference at the time of sanction suggests that excessive effort, induced by a losing position, is an important influence on award of yellow and red cards. Controlling for a number of pre-game and within-game variables, we find evidence of home team favouritism in Germany as home teams with running tracks in their stadia attract more yellow and red cards than teams playing in stadia with separation of fans from pitch. This is indicative of referee response to social pressure. Separating the competing teams in matches by favourite and underdog status, as perceived by the betting market, yields further evidence, this time for both leagues, that the source of home teams receiving fewer cards is not just that they are disproportionately often the favoured team. Rather, there appears to be pure referee bias in relative treatments of home and away teams.