Does the Video Assistant Referee (VAR) mitigate referee bias on professional football?

Abstract

The purpose of the paper is to check whether the introduction of the VAR system mitigated the referee bias against away teams. The dataset comprises 2279 matches played in the first tier of the Brazilian League from 2016 to 2021. We analyze 6 seasons of the first tier of the Brazilian domestic football league- 3 seasons before and 3 seasons after the introduction of the VAR technology. Potential bias is viewed through the lens of yellow cards, red cards and number of penalties awarded for both home and away clubs. A paired t-test is used to reveal potential statistical differences between pre-VAR and post-VAR periods, followed by Ordinary Least Squares regressions to inspect whether certain referee' categories have changed their behavior after the implementation of this technology. Our empirical findings offer evidence that the referee bias is diminished, but still present.