## 4 Discussion  
We investigated the differences between match performance indicators in the Turkish Super League with and without VAR and analyzed the effect of VAR on these variables in each season following the implementation of the VAR system. The results of our study revealed that VAR resulted in significant changes in some aspects of the game in the Turkish Super League. Fouls, yellow cards, and offsides significantly decreased after the introduction of VAR, while penalties significantly increased. However, VAR technology did not affect the number of goals or red cards. While some variables showed statistically significant changes after the implementation of VAR, it is important to interpret these results in the context of their effect sizes. For example, the reduction in fouls demonstrated a large effect, suggesting a substantial behavioral change. In contrast, yellow cards, offsides, and penalties showed small effect sizes, indicating that although the direction of change was consistent, the actual per-match differences were modest. This reinforces the importance of complementing \(p\)-values with measures of practical significance, especially in large-sample studies where even small differences can reach statistical significance. Our generalized linear models helped clarify these nuances by quantifying the relative strength of VAR's influence across different performance indicators. As expected, players seemed to adapt their behavior, committing fewer fouls and offsides and receiving slightly fewer yellow cards. In contrast, the number of goals did not significantly decrease, possibly due to the balancing effect of goals awarded and disallowed after VAR review. After all, referees were expected to make the most incorrect decisions in goals. As the goals are reviewed and confirmed by VAR or a review is suggested on the field, a decrease in the number of goals conceded would have been expected. However, our results showed that the number of goals conceded slightly decreased after VAR, but this decrease was not statistically significant. Penalties and red cards are important decisions that are missed by referees on the field and therefore would have been expected to increase with the assistance of VAR. While penalties increased as expected, no significant changes were observed in red cards. The most important reason for this may be that the number of red cards is rare during a football match. In addition, football players may have been more cautious due to the chance for referees to re-evaluate their decisions with the help of VAR. Furthermore, significant changes in match performance indicators would have been expected in the seasons after the implementation of VAR. However, apart from fouls, there were no significant changes in other match performance indicators. This may be a result of the teams' performances, technical and tactical skills, and the effects of VAR on referee decisions. Although various technological assistants such as additional assistant referees, goal-line technology, and headset systems have been used over time to compensate for incorrect decisions by football referees during matches [6; 7], there are still some obvious errors that cannot be prevented. To address this problem, VAR was introduced in 2018, a system that allows referees to review their decisions by watching their clear and obvious errors via video. The introduction of the VAR system has sparked great controversy [15]. Some believe that it will make the game fairer, while others are concerned that it may interfere with the flow and spirit of the game [27]. The use of VAR results in more time-outs and matches lasting longer [10], which leads to a decrease in players' motivation and performance [28]. However, the VAR system has also had a positive impact on the accuracy and consistency of referees' decisions. Referees are able to make more informed and accurate decisions using video evidence [18; 19]. In this study, the number of fouls significantly decreased, while the decrease in yellow cards was minimal.