The Covid-19 pandemic has induced worldwide natural experiments on the effects of crowds. We exploit one of these experiments currently taking place over several countries in almost identical settings: professional football matches played behind closed doors. We find large and statistically...

Competitions often suffer from biased judgments by officials tied to their social identities. In international cricket, home nation umpires favoured home teams, but neutral umpires were introduced successfully to address this bias. However, the COVID-19 pandemic prompted the return of home...