Home advantage bias in yellow card allocation in Brazilian soccer

Abstract

Home Advantage is a relevant research topic across various sports, including soccer. It refers to the tendency for the home team to perform better than the visiting team, influenced by factors such as match performance and environmental variables such as referees' decisions on yellow cards. However, the factors influencing yellow card bias favoring home teams in Brazilian soccer remain unclear. This study aimed to determine whether variables such as a new stadium format, championship structure, crowd presence, and differences in team rankings affect referees' yellow card bias. To investigate this, 2,242 official match summaries from the Brazilian National Championships during the 2014–2018 seasons were analyzed. The number of yellow cards was analyzed according to (i) geography (visiting vs. home team), stadium format (pure soccer vs. track & field stadiums; traditional vs. arena stadiums), championship configuration (cup vs. league), and (iv) ranking team difference calculated accordingly: visiting ranking – home ranking. The visiting teams received more yellow cards than the home teams in both championships (p < 0.001), but the public crowd did not affect yellow card referees’ bias (p = 0.114). In contrast, ranking team differences significantly affect yellow card referees’ bias (p < 0.001), with a greater yellow card referees’ bias in matches with greater ranking team differences. The stadium format just affects yellow card referees’ bias when classified as traditional or arena stadiums (p = 0.010), and yellow card referees’ bias was greater in the Arena than in Traditional Stadiums. In addition to these results, independent of the ranking team differences, the yellow card referees’ bias is around 80% greater in Cup than League. Therefore, yellow card referees’ bias is present in the Brazilian National Championships, and stadium format, championship configuration, as well as raking team differences, affect this bias.