How Much of ‘Home Field Advantage’ Comes from the Fans? A Natural Experiment from the COVID-19 Pandemic

Home field advantage has been a commonly accepted assumption in sports. How much of this advantage is due to the home team’s supporters’ physical attendance at the game where they might encourage their team, intimidate the opponent, and influence game officials? We utilize the unique natural experiment of the COVID-19 pandemic and consider the case of American professional (NFL) and collegiate (NCAA) football to examine this question. We measure how typical spreads, relative to home teams, changed in the 2020 season compared to their historical levels, and we determine that roughly half of what football fans and analysts consider to be home field advantage emanates from spectators. Generally the betting market was rather accurate in its predictions of how football game results would change in 2020, during the pandemic, so that wagering strategies failed when based on the betting market possibly underappreciating or overcorrecting for home field advantage without fans.