Major League Baseball during the COVID-19 pandemic: does a lack of spectators affect home advantage?

Winning in professional sports is crucial for financial success, leading to extensive research on factors influencing victory. While advancements in training, technology, and analytics provide temporary advantages, one consistent factor remains: game location. The "home advantage," where home teams win over 50% of games, is well-documented across major sports leagues. Several factors contribute, including crowd support, familiarity with facilities, travel fatigue, and psychological factors. The COVID-19 pandemic provided a unique opportunity to study the role of spectators, as many leagues, including MLB, resumed games without fans. Prior research on the impact of spectator absence on home advantage in other sports, particularly European football, yielded mixed results. This study aimed to investigate the impact of spectator absence on home advantage in MLB during the 2020 season, comparing it to data from 2015-2019, hypothesizing that the relatively low home advantage in MLB would be less affected by the lack of spectators than in other leagues.

Existing literature highlights the consistent home advantage across various professional sports leagues, with MLB exhibiting one of the lowest home winning percentages. Several factors have been proposed to explain this advantage, including crowd support impacting player performance and psychological states (positive for home teams, negative for visitors). Other factors include familiarity with facilities, travel fatigue, and various psychological and physiological factors. However, disentangling these factors' individual effects is challenging due to their co-occurrence. The COVID-19 pandemic, forcing spectator-less games, offered a unique natural experiment to assess the role of spectators. Previous studies investigating the impact of this change on home advantage in European football showed mixed results, with some finding no significant change and others observing a decrease or even a reversal of the home advantage.

Data on MLB regular-season games from 2015-2020 were obtained from Retrosheet, encompassing 13,044 games (898 in 2020, 12,146 in 2015-2019). Home advantage was assessed using three variables: a game-level dummy variable for home-team wins, a team-level variable for the percentage of home games won, and a relative home advantage variable (percentage of home wins out of total wins) to account for team quality. Team quality was measured using the sum of Wins Above Replacement (WAR) for all players, categorized into tertiles. Attendance was represented by the attendance ratio (average attendance/stadium capacity), categorized into quartiles. Logistic regression was used to compare home advantage with and without spectators at the game level, with year (2020 vs. 2015-2019) as the independent variable. One-way ANOVA was used to compare relative home advantage across years, team quality, and attendance ratio. Factorial ANOVA explored interactions between these variables. SAS and SPSS were used for data analysis, with p<0.05 considered statistically significant.

Descriptive statistics showed average home advantage ranging from 52.77% to 54.98%, consistent with previous research. Mean relative home advantage was significantly higher than 50% in all seasons. Logistic regression revealed that the odds ratio for a home-team win in 2020 compared to 2015-2019 was 1.068 (p=0.344), indicating no significant difference. One-way ANOVA showed no significant difference in relative home advantage across years, team quality (WAR), or attendance ratio. Factorial ANOVA models, including year, WAR, and attendance ratio, also revealed no significant effects or interactions on relative home advantage.

The findings suggest that the absence of spectators did not significantly affect home advantage in MLB, indicating that crowd support may not be a crucial factor in this league. This contrasts with some studies on other leagues (European football, NBA) that reported more significant crowd effects. The consistent home advantage in MLB over many years, averaging around 54%, further supports this conclusion. The use of relative home advantage, controlling for team quality, strengthens the results' robustness. This suggests that other factors, such as familiarity with playing facilities or travel fatigue, might play more significant roles in MLB's home advantage than crowd support.

This study demonstrates that the absence of spectators during the 2020 MLB season did not significantly impact home advantage. This contrasts with findings from other sports, potentially due to differences in fan culture and behavior. Future research should investigate other contributing factors like facility familiarity and travel fatigue, while also accounting for other pandemic-related changes in the 2020 season, such as schedule alterations and rule changes.

The study employed a quasi-experimental design, using the 2020 season as a natural experiment. This season had unique characteristics beyond the absence of spectators, such as a shortened schedule, altered opponent matchups, and rule changes. These factors might have confounded the results, making it difficult to isolate the specific effect of spectator absence. Additionally, teams implemented strategies to simulate crowd noise and atmosphere, which weren't controlled for in the analysis.