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...

A detailed longitudinal dataset is assembled containing annual performance and biographical data for every player over the entire history of professional major league baseball. The data are then aggregated to the team level for the period 1920-2009 in order to test whether teams built on a more...