War, identity, and referee bias: Evidence from professional football.

This study analyzes whether and how the war between Russia and Ukraine has influenced referee behavior in UEFA football competitions. Exploiting the exogenous shock repre sented by the outbreak of the conflict in February 2022, we adopt a TWFE model using detailed match-level data for the period 2015–2025. The results show that Russian players are significantly more likely to receive red cards when officiated by referees from Ukraine or from countries strongly aligned with Ukraine. In contrast, players from countries with ambiguous geopolitical positions receive fewer foul calls when refereed by Ukrainian of f icials. We also document a reverse bias. These effects are not driven by nationality matching between referees and players, nor by a general increase in referee strictness, but rather reflect selective identity-based distortions linked to political alignment. The bias is particularly evident in high-discretion decisions and takes different forms, ranging from visible sanctions to more subtle omissions. Overall, the findings suggest that geopolit ical conflicts can activate behavioral distortions even in regulated and formally neutral settings, such as international sports.