This study investigated longitudinal changes in playing time of U22 players following the introduction of the U22 regulation in K League 1, the top division of professional football in Korea. The analysis covered six seasons from the 2019 season when the regulation was first implemented to 2025. A total of 1,188 matches were included, excluding post season split matches. On average, 1.46 U22 players per team participated in each match during the 2019 season, with the highest average observed in 2022 (2.32 players). In the most recent season (2025), the average number of U22 players per match was 1.99. Mean playing time per U22 player was highest in 2019 (66.8 minutes per match), decreased to its lowest level in 2021 (47.0 minutes), and slightly increased to 49.5 minutes in 2025. Approximately 20% of U22 players who started matches were substituted during the first half, and 13.8% were substituted within the first 30 minutes of play. No statistically significant differences in playing time were found according to match location (home/away) or match outcome (win/draw/loss). However, significant differences were observed across team strength levels (strong/medium/weak team). Furthermore, seasonal variations in U22 players’ playing time appeared to be strongly influenced by annual modifications to the detailed regulations. By providing objective and quantitative evidence on player participation since the introduction of the U22 regulation, this study offers an empirical basis for evaluating the current system. The findings contribute to discussions on potential policy improvements and provide practical implications for the future development of the regulation.
Kim et al. (Sat,) studied this question.