OWN‐NATIONALITY BIAS: EVIDENCE FROM UEFA CHAMPIONS LEAGUE FOOTBALL REFEREES

I. INTRODUCTION Athletes continually search for ways to obtain even the slightest advantage over their opponents. It is often these slim margins that make the difference in competitive games and leagues. League officials have the responsibility to organize and monitor leagues such that no unfair advantage is gained by any particular player or team. Similarly, referees in football, and in most sports, are hired precisely for the purpose of officiating matches with objectivity, and to provide a fair playing environment. However, sometimes referees, whether consciously or subconsciously, exhibit a systematic bias for or against players due to their race, gender, nationality, or other characteristics. In this paper, we address whether own-nationality bias is exhibited by referees toward professional football (soccer) players in the UEFA Champions League (UCL). We also explore how different types of players and settings affect the magnitude of the own-nationality bias. These players and settings include national team players, players at home, matches officiated by the most elite referees, and in later stages of the tournament. Lastly, we look at how much, if any, of the identified own-nationality bias is due to cultural or linguistic similarities. The data consist of 12 seasons of player-match specific information from the UCL, which is one of the most prestigious professional club football tournaments in the world and brings in over 1.1 billion [euro] in annual revenue. The UCL tournament consists of 10 months of matches with 76 of the best club teams in Europe. It provides a window into high stakes, competitive, and scrutinized interactions between 402 of the most highly trained football referees and 4,294 of the best football players in the world, all from a total of 105 countries. UEFA assigns referee squads composed of 4-6 referees from the same country to tournament matches such that a referee squad's nationality is different than that of the nationality of either of the two teams being officiated. This method of assignment allows for our identification strategy to detect whether referees exhibit favoritism toward players from their same country, or in other words, own-nationality bias. Although no referee squad and team are from the same country, oftentimes there are individual players who are from the same country as the referee squad. These same country pairings of referee squads and individual players allow for a within-player analysis of referees' own-nationality bias. For a specific player across games, we compare the fouls called by a referee squad from his home country to the fouls called by a referee squad not from his home country. We find that players in a same country referee-player pairing receive more favorable foul calls than when they are not in a same country referee-player pairing. On average, having a referee squad from the same country increases the number of beneficial foul calls received by a player by about 10%. The amount of own-nationality bias exhibited by referees is more pronounced (15-20%) for national team members, when players are playing at their home venue, for the highest qualified referees, and during the later stages of the tournament. We also find that the own-national bias found cannot be solely attributed to similarities in language or culture of referees and players from the same country. There are two particularly pertinent studies that analyze racial bias in athletics. Price and Wolfers (2010) show that in the National Basketball Association (NBA), more personal fouls are called against players when they are officiated by an opposite-race refereeing crew than when they are officiated by an own-race refereeing crew. Also, Parsons etal. (2011) find that an umpire calls fewer strikes when the pitcher is of a different race than the umpire. They also show that this is particularly true when there is low scrutiny of the officiating. …