In this paper, we test for, and find evidence of, referee bias in favor of home teams in European football using minute-by-minute analysis to control for within-game events. The context for the analysis is Spain's Primera Liga and the Union of European Football Association (UEFA) Champions League. We find that the award of sanctions by Spanish referees in the Champions League are not significantly different to those of the referees from other countries and as such are subject to the same sources of bias. In Primera Liga matches where the crowd is separated from the pitch by running tracks, we find that the probability of the award of a yellow card to the home team is higher and that of the away team is lower compared to matches played at stadia without running tracks. Similar results are found in the Champions League, where efforts are made to hire “neutral” referees. Referee behavior is also influenced by the size of the crowd in attendance.