The Covid-19 pandemic has induced worldwide natural experiments on the effects of crowds. We exploit one of these experiments that took place over several countries in almost identical settings: professional football matches played behind closed doors within the 2019/20 league seasons. We find large and statistically significant effects on the number of yellow cards issued by referees. Without a crowd, fewer cards were awarded to the away teams, reducing home advantage. These results have implications for the influence of social pressure and crowds on the neutrality of decisions.

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Because maximizing stadium attendance demand is of utmost importance, for both sports economists and sport management researchers, understanding the potential determinants of such demand better has become a priority in the last decades. Here, conducting a systematic scoping review, we map this previous research in terms of its characteristics, its nature, and its volume, thus offering a concise perspective on what has been previously explored, and, more importantly, what remains to be analyzed in the future. Intriguingly, we observe a lack of studies exploring data generated in both niche and women’s sports, as well as in most emerging markets. Further, the field has not yet established the use of disaggregated stadium attendance data, despite notable potential methodological pitfalls.

We use a series of natural experiments in association football (soccer) to test whether the lack of social pressure from spectators affected behaviour and outcomes. We observe that the normal advantage to the home team from playing in their own stadium was on average eroded when they played behind closed doors, with no supporters. Among the various effects from no fans being present, visiting players were cautioned significantly less often by referees. This suggests that closed doors matches are different because referees favour the home team less in their decision making. We discuss these findings in the light of the Covid-19 pandemic that has led to the remainder of the 2019/20 European football season playing out in empty stadiums.

We use a series of historical natural experiments in association football to test whether social pressure from a home stadium crowd affected behavior and outcomes. The standout effect of an empty stadium was that referees cautioned visiting players less often, by over a third of a yellow card per match or once for every 22 fouls committed. Stadium crowds caused referees to favor the home team in their decision-making. Empty stadiums appear to have reduced the overall home advantage in the final outcomes of football matches, but we cannot statistically reject no effect.