By Divij Jain ’21
For the first time ever, there is data to determine the true magnitude of the impact of fans on the outcome of a soccer match.
As the COVID-19 pandemic forced soccer games across Europe to be played behind closed doors, teams were forced to grapple with the unfamiliarity of playing without being surrounded by thousands of spectators. Based on data collected from the 2019/20 German Bundesliga and English Premier League seasons, the absence of fans has certainly had an impact on match proceedings—an impact that has reduced home team advantage significantly.
There is an undisputed home team advantage in soccer, and it can be attributed to a number of components: travel, familiarity, and, of course, the fans. Away teams are often exhausted from hours of travel, less familiar with the field and stadium than the home team, and subjected to 90 minutes of psychological torture from the home team’s fans, all of which put them at a disadvantage. There was no way of determining for certain which component was the primary cause of the home team advantage—until now.
As COVID-19 spread rapidly through Europe in March, domestic leagues and continental competitions paused indefinitely. Some leagues, such as France’s Ligue 1, decided to cancel the season entirely, but most decided to take the risk to finish the season. In May, the Bundesliga became the first high-profile league to resume, and the Premier League followed in June. Although the leagues continued, fans were not allowed back in the stadiums.
Prior to the COVID-19 hiatus, the home advantage was present in the Bundesliga and Premier League as expected. Bundesliga teams won 43% of home games and lost 35%, and Premier League teams won 45% of home games and lost 30%. When playing without fans, these numbers changed drastically in the Bundesliga (32% wins and 45% losses) but stayed roughly the same in the Premier League (47% wins and 32% losses).
The difference in the number of goals scored between the home and away team can measure the psychological impact of the home fans on the players. Before the break, Bundesliga home teams outscored their opponents by 0.241 goals per game on average, and Premier League home teams outscored their opponents by 0.292 goals on average. Without fans in attendance, Bundesliga home teams actually scored 0.244 goals fewer than their opponents on average, while Premier League home teams continued to outscore their opponents, now by 0.370 goals on average.
From match outcome and goal statistics, there is strong evidence that Bundesliga fans have a significant impact on the players, so much so that away teams seemed to develop an advantage of sorts after the COVID-19 hiatus. In the Premier League, on the other hand, results and goal statistics remained largely unchanged. It seems that in the Bundesliga, fans play a much larger role in creating the home advantage than in the Premier League.
In addition to affecting players, hostile home fans have the ability to psychologically impact and bias referees towards their team, which can, in turn, change the outcome of a game. One way to measure referee bias is by comparing the number of yellow cards home teams receive compared to away teams. Unlike penalties or red cards, the newly instated Video Assistant Referee (VAR) does not have any say in awarding or overturning yellow cards; in other words, yellow card decisions are under the full discretion of the on-field referee.
Prior to the break, Bundesliga home teams earned 0.344 fewer yellow cards than their opponents per game on average, and Premier League home teams earned 0.285 fewer yellow cards than their opponents on average. Once the league resumed, Bundesliga home teams earned 0.159 more yellow cards than their opponents on average, and Premier League home teams earned 0.033 more yellow cards than their opponents on average.
In both leagues, the initial difference between home team and away team yellow cards became much closer to zero when teams were playing in empty stadiums. There is no reason why away teams should earn more yellow cards than home teams, so the most obvious cause of the difference is the influence that home fans have on biasing the referee to inadvertently favor their team.
So what do these statistics mean for the sport as a whole? If this “new normal” continues through a large part of next season, what should fans expect to see? Will teams that have smaller home stadiums (e.g., compare Union Berlin’s stadium capacity of 22,000 to Borussia Dortmund’s 81,000) have an advantage, as they as not used to relying heavily on huge numbers of home fans? Will Liverpool lose a league home game for the first time since April 2017? Even once fans return, how will the leagues combat inadvertent referee bias? Will we see the expansion of VAR until human input plays little to no role in refereeing? Only time will tell.