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In wake of the Covid-19 pandemic, 2019-2020 soccer seasons across the world were postponed and eventually made up during the summer months of 2020. Researchers from a variety of disciplines jumped at the opportunity to compare the rescheduled games, played in front of empty stadia, to previous games, played in front of fans. To date, most of this post-Covid soccer research has used linear regression models, or versions thereof, to estimate potential changes to the home advantage. However, we argue that leveraging the Poisson distribution would be more appropriate and use simulations to show that bivariate Poisson regression (Karlis and Ntzoufras in J R Stat Soc Ser D Stat 52(3):381-393, 2003) reduces absolute bias when estimating the home advantage benefit in a single season of soccer games, relative to linear regression, by almost 85%. Next, with data from 17 professional soccer leagues, we extend bivariate Poisson models estimate the change in home advantage due to games being played without fans. In contrast to current research that suggests a drop in the home advantage, our findings are mixed; in some leagues, evidence points to a decrease, while in others, the home advantage may have risen. Altogether, this suggests a more complex causal mechanism for the impact of fans on sporting events.

The present paper investigates factors contributing to the home advantage, by using the exceptional opportunity to study professional football matches played in the absence of spectators due to the COVID-19 pandemic in 2020. More than 40,000 matches before and during the pandemic, including more than 1,000 professional matches without spectators across the main European football leagues, have been analyzed. Results support the notion of a crowd-induced referee bias as the increased sanctioning of away teams disappears in the absence of spectators with regard to fouls (p < .001), yellow cards (p < .001), and red cards (p < .05). Moreover, the match dominance of home teams decreases significantly as indicated by shots (p < .001) and shots on target (p < .01). In terms of the home advantage itself, surprisingly, only a non-significant decrease is found. While the present paper supports prior research with regard to a crowd-induced referee bias, spectators thus do not seem to be the main driving factor of the home advantage. Results from amateur football, being naturally played in absence of a crowd, provide further evidence that the home advantage is predominantly caused by factors not directly or indirectly attributable to a noteworthy number of spectators.

We analyze the natural experiment of ghost games in the 2019/2020 season of the German football Bundesliga and confirm previous studies showing that the home advantage diminishes if the stadium is empty. However, our paper is the first that distinguishes between effort- and skill-based tasks in this setting. In line with behavioral economics, we observe that a supportive audience has a positive effect on effort-based performance but a negative effect on some offensive skill-based performance measures.

Background: The role of cheering in home advantage in sports performance is the subject of much debate. No definitive scientific evidence has so far been found capable of highlighting or denying its relevance. As pandemic restrictive measures (COVID-19) have prevented crowds from entering stadiums, analysis of the past two football seasons may reveal important new details. Objective: This paper aims to compare the statistics of the last two football seasons in Italy with the previous six, trying to highlight any pronounced and statistically significant changes due to the absence of cheering in the stadiums. Methods: We compared the average percentages of points obtained in home matches from 2013 to 2019 with those in the timelapse 2019-2021. The same operation was performed with referee statistics, such as fouls, penalties, and cards awarded against home teams. To do this, we used measures such as Welch's t-test and percentage increases. The distributive normality of the datasets was evaluated with the Shapiro-Wilk test and a graphical control. The lack of trend in the series was assessed with the Mann-Kendall test and Sen's Slope. Finally, Pearson and Spearman's correlations were searched between the percentages of points collected in home matches and total points, year by year, from 2013 to 2021.Results: The average percentage of points collected by teams in home matches dropped by almost 8% (Welch’s t-test = -4.3). Moreover, the negative correlations between home collected points and total points in 2013-2019 timelapse have drastically diminished during the last two seasons (average Welch’s t-test = 6.0, 95% CI: 5.4 – 6.4), approaching zero. Finally, penalties against home teams have increased by 30% (Welch’s t-test = 2.6), reaching figures closer to 50%.Conclusions: This research provides statistical evidence in favor of the relevance of home advantage in the top football league in Italy, such as Serie A. During the anti-COVID-19 restrictive measures - which prevented public access to the stadiums - a net reduction in the points collected by the teams in home matches was detected. In addition, the number of penalties awarded against home teams has increased significantly, approaching the ideal 50%. Since there are valid psychological reasons in the literature to support the crowd’s impact on sports and refereeing performance, it is plausible that our findings are causally related to the absence of cheering. Finally, as the averages of points collected at home remained far from 50%, our results suggest that a not negligible part of the home advantage in Serie A is linked to factors independent of the audience. Future research can deepen the above phenomena from a theoretical-psychological point of view.

Covid-19 pandemic forced, at the final rounds of 2019–2020 season, in many different sport leagues worldwide, teams to play without an audience. Therefore, the present paper aims to compare the home advantage score in the last ten rounds in 2019–2020 season with the first 24 rounds in same season using Pollard’s (1986) and Matos et al.’s (2020) methods. In addition, comparisons across different seasons (2016–2017, 2017–2018, 2018–2019 and 2019–2020) using the same methods were also analyzed. Results showed no differences (p &gt, 0.05) between first 24 rounds and the last 10 in 2019–2020 season as well as in the 3 previous seasons. With Pollard’s method, no differences (p &gt, 0.05) were also found among those four seasons on global (all 34 rounds) home advantage. However, a significance difference between 2017–2018 and 2019–2020 (p &lt, 0.05) was founded using Matos et al.’s (2020) method, which is an indicator of the importance of using complementary methods when analyzing the same realities. Overall, despite what might be expectable from recent findings, the lack of an audience in the last 10 rounds of Portuguese Football League 2019–2020 season, due to COVID-19 pandemic, did not affect home advantage. Therefore, future studies could try to analyze other different variables in Portuguese Football League, such as referees’ behaviors, rules changing (e.g., the possibility of making five substitutions, instead of three), crowd dimension and density as well as include variables about odds as forecasts in football being played without crowds.

Social pressure may have relevant consequences in many contexts but it is hard to evaluate it empirically. In this paper we exploit a natural experiment in soccer to provide clear evidence of its effects. We aim to study how social pressure from the crowd in a stadium affects both players and referees. While in normal matches crowd support may be correlated to a host of variables affecting the outcome of interest, we exploit the fact that after the health emergency for the Covid-19 pandemic in 2020, soccer matches in top European Leagues have been allowed only behind closed doors, that is, without spectators in the stadiums. We use data of first and second division of 5 major European Leagues (Germany, Spain, England, Italy and Portugal) for the last 10 championships and compare several outcomes (determined by players' performance and referees' decisions) of matches played with crowd support to the same outcomes when matches were played without crowd. We find considerable effects of the pressure from the crowd: while with the support of the crowd a considerable home advantage emerges in various measures of performance (points, goals, shots, etc.), this advantage is almost halved when matches are behind closed doors. Similar effects are found for the behavior of referees: decisions of fouls, yellow cards, red cards and penalties that tend to favor home teams in normal matches, are much more balanced without crowd pressing on referees. The evidence we provide strongly supports the idea that social pressure has intense effects on agents' behavior.