The 12th Man Plays Defense: The Effects of Heterogeneous COVID-19 NFL Stadium Attendance Restrictions

Using heterogeneous COVID-19 stadium attendance restrictions during the 2020 NFL season as an instrumental variable for stadium attendance and a novel panel data containing historical NFL game outcomes, attendance, weather, penalty assessment and visitor travel information between 2009 and 2022, I examine the effect of home stadium attendance on a variety of match outcomes, while controlling for a comprehensive set of covariates. I find that home stadium fans influence the outcomes of NFL games in favor of the home team, and that this result is insensitive to the inclusion of other factors previously suggested to explain home advantage in gridiron football. Neither the size of the home crowd nor the home crowd density has any measurable effect on referee home bias in the NFL, suggesting NFL home fans directly influence match outcomes by negatively affecting visiting team performance, possibly through a crowd noise distraction mechanism.