Once or twice? The effect of different number of video assistant referees intervention

The Chinese Football Super League (CSL) introduced the video assistant referee (VAR) in the 2018 season, but the effect of VAR intervention has not yet been analyzed. The purpose of this study is to explore how varying frequencies of VAR interventions affect performance indicators in the CSL. VAR interventions were categorised into three groups, none (VAR0 = 198), one (VAR1 = 184) and two or more (VAR2 = 194). The performance variables included scoring-related variables (goals, shots, shots in the penalty area and penalties), attacking and passing-related variables (passes, crosses and free kicks) and defensive-related variables (tackles, fouls, yellow cards and red cards). The Kruskal-Wallis tests were used to examine the differences in performance variables among the different groups. The findings of these tests revealed that VAR was used in 66% of matches in the 2019–2021 season of the CSL. There were significant differences in penalties (p < 0.01, η² = 0.11), shots (p < 0.05, η² = 0.03), shots in the penalty area (p < 0.01, η² = 0.01), fouls (p < 0.01,η² = 0.02), passes (p < 0.01,η² = 0.05), free kicks (p < 0.05, η² = 0.01) yellow cards (p < 0.01, η² = 0.02) and red cards (p < 0.01, η² = 0.05), but there were no significant differences in the number of goals (p > 0.05), crosses (p > 0.05) and tackles (p > 0.05). Therefore, VAR intervention was frequently applied in the CSL during the 2019–2021 season, and the VAR interventions had various impacts on performance indicators.