Eliminating supportive crowds reduces referee bias

We use a series of historical natural experiments in association football to test whether social pressure from home stadium crowd affected behavior and outcomes. The standout effect an empty was that referees cautioned visiting players less often, by over third yellow card per match or once for every 22 fouls committed. Stadium crowds caused favor the team their decision-making. Empty stadiums appear have reduced overall advantage final outcomes matches, but we cannot statistically reject no effect.