Objective Youth soccer injury can be prevented through various means, but few studies consider the role of referees. Following previous research suggesting children take fewer risks when supervised intensely, this randomized crossover trial evaluated whether risky play and injuries decrease under supervision from three referees instead of one referee. Methods Youth soccer clubs serving a metropolitan U.S. area participated. Boys' and girls' clubs at under age 10 (U10) and under age 11 (U11) levels were randomly assigned such that when the same clubs played each other twice in the same season, they played once with one referee and once with three referees. A total of 98 games were videotaped and subsequently coded to obtain four outcomes: collisions between players, aggressive fouls (involving physical player-to-player contact) called by the referee(s) on the field, aggressive fouls judged by trained coders, and injuries requiring adult attention or play stoppage. Results Poisson mixed model results suggest players in the 98 games committed fewer aggressive fouls, as identified independently by referees (rate ratio [RR] 0.58; 95% confidence interval [CI] 0.35-0.96) and by researchers (RR 0.67; 95% CI 0.50-0.90), when there were three referees versus one referee. Collisions (RR 0.98; 95% CI 0.86-1.12) and injury rates (RR 1.15; 95% CI 0.60-2.19) were similar across conditions. Conclusion When the same youth soccer clubs played with three referees rather than one, they committed fewer aggressive fouls. More intense supervision created better rule adherence. Injury rates were unchanged with increased supervision. Results raise questions concerning whether financial investment in additional referees on youth soccer fields yields safety benefits.