The influence of spectators on home advantage and referee bias in national teams matches: insights from UEFA Nations League

The home advantage and the subconscious referee bias regularly occur in professional sports, particularly in association football. The matches played behind closed doors in spring and summer 2020 highlighted that the crowd support is one of the main factors contributing to both phenomena in domestic leagues. The aim of the present study was to investigate whether the same applies also to national teams matches, given the different impact of the other factors determining the home advantage in such matches. To this purpose, the 2018-19 and the 2020-21 editions of the UEFA Nations League - 133 matches each - were analysed, the former played in front of spectators while the latter with no or limited attendance. In particular, we examined a set of indicators of home advantage (match outcome, points, goals scored, ball possession, total shots, shots on goal, corner kicks) and of referee bias (fouls, yellow cards, red cards, penalty kicks, extra time), controlling for the FIFA World Ranking points and the number of time zones crossed. Comparing home and away teams on these parameters within each edition, we observed the occurrence of both phenomena in 2018-19, as well as their absence in 2020-21. Moreover, the comparison between the two editions revealed a significant reduction of both phenomena. The results indicate that spectators have a decisive role in contributing to both the home advantage and the referee bias in national teams matches.