Home field advantage is universally accepted across most major sports and levels of competition. However, exact causes of home field advantage have been difficult to disentangle. The COVID-19 pandemic offers a unique, natural experiment to isolate elements related to home field advantage since all 2020 regular season Major League Baseball games were played without fans. Results provide no statistically significant evidence of a difference in home field advantage between the 2019 and 2020 seasons, evidence that home crowd support is not a driver of home field advantage. There does appear to be a statistical advantage by the home team batting second in the inning. Travel fatigue seems to have no impact on home field advantage, and while home field advantage seems to increase throughout the 2020 season, we chalk that up to small sample noise. Despite lacking historical precedence, betting markets seemingly respond efficiently to the new home conditions. Keywords: home field advantage, market efficiency, baseball, ghost games
