A influência do viés arbitral doméstico nos jogos da Copa Libertadores da América

Abstract

The Copa Libertadores da America (CLA) is an international competition that involves the champion teams and the best ranked teams from each country of South America. Thus, it would be a problem the existence of an unbalanced competition due to referee bias, a phenomenon noticed in various sports events. Thus, the objective of this study was to verify the effect of referee bias in CLA in the 2018 and 2019 seasons (n=222 games). The dependent variables for univariate statistic inferences were the disciplinary sanctions (fouls, yellow card, red card, and penalties); and two derivative indices for pondered magnitude of the disciplinary sanctions and the referee in the home-away delta format, [e.g., “disciplinary sanctions (delta)” and “referee decisions (delta)”]). For modeling and adjustment of referee bias, binary logistic regression was used, being “audience” (audience) and occupation rate, ball possession, finishes, and “referee decisions (delta)”, and the stage competition as independent variables; success of the home teams (e.g. victory) as dependent. Referee bias was evidenced, noticing more frequent disciplinary sanctions for the away team in yellow cards (0.14; p=0.015) and more frequent penalties for the home team (1.94; 74.6% of the total penalties). For the “referee decisions (delta)” variable, it was noticed 0.90, where the positive values represent favoring for the home teams. There were no significant univariate correlations between “referee decisions (delta)” and “audience”; as the rate of stadium occupation (p>0.05). The results of the final modeling indicated three predictor variables in the adjust and the first (“audience”, “stadium occupation (%)” and “stage competition”). The odds ratios indicated an important increase in the chance of of home teams wins from each unitary change in “referee decisions (delta)” with a magnitude of 26% (OR 1.26 [95%IC= 1.15, 1.41]; p<0.001). Such findings of referee bias could be related to “home advantage” observed (69.8%-point average for the home team). The findings of this study could help in the improvement of the training for the referee and his performance in hostile environments. This study concludes that exists a referee bias in CLA, with no direct relation with the crowd effect.