ABSTRACT
Abstract Aims: The present study aimed to analyze the effects of the 3- and 6-substitution rule and qualification round on substitution pattern, game statistics, win rate, and winning probability in Brazil's largest U-20 football tournament. Methods: We analyzed 1,339 matches from the São Paulo Junior Football Cup implementing a before-after design considering 6 years (three seasons for 3-subs and three for 6-subs). Results: Approximately 31% of teams used the total number of replacements of 6-subs with the same substitution pattern between rounds. The win rate for both substitution rules was approximately 79% (OR = 3.10, 95%CI [2.18, 4.51]) with a small reduced magnitude (approximately 5%) in 6-subs knockout games. Logistic regression analysis showed that the 6-subs regulation tournament predicted a reduced probability (-12%) of a match ending with a win in the knockout round. There were 6-subs knockout effects (p < 0.05) on game statistics with "negligible" effect size (ES) on "effective playing time" (+1 min; ES = 0.15); decreased "goal scoring" (-0.3;ES = 0.09) and "red cards" per match (-0.1; ES = 0.06). An ordered probit model and partial effects showed that including a replacement unit on a team increased the winning probability by 8% in the group stage, and reduced the chance (-4%) for the opponents trying to do the same in the knockout stage. Conclusion: Overall, 6-subs caused minor effects on the game statistics, win rate, and winning probability. Understanding substitution strategies and motivation, individual and collective performance effects, and whether there will be changes in the game profile will become relevant research issues when a greater number of substitutions rules are universally instituted.