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...

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...