AbstractObjectiveThe development of a brief online program to improve prosocial parent behavior at children's sporting events is described. We provide an overview of the collaborative research and development process, the theoretical basis for program content, design features, and evaluation approach used to establish the feasibility of Play Well Triple P in Junior Rugby League.BackgroundParents influence children's experience of sports, impacting their enjoyment and participation, motivation to play, behavior, and performance during sporting events. Parental expectations and behaviors can place pressure on children, decreasing their enjoyment and contributing to their desistance from playing sport. As sport is important for maintaining children's social and psychological well‐being, research is needed to investigate strategies for supporting children to retain positive involvement in sports throughout childhood and adolescence.MethodCodesign principles were applied across four phases of program development—surveying parents of junior players (Phase 1), which informed the development of program content and design (Phase 2), refining the program based on feedback from parents and sports officials (Phase 3), and concluding with a feasibility evaluation of the final program (Phase 4).ResultsParents who participated in Play Well Triple P reported improvements in positive sport parenting behavior, decreases in negative sport parenting behavior, and a high level of satisfaction with the program.Conclusions and implicationsThe codesign framework for the development of a parent program for rugby league produced a promising and well‐accepted sports parenting program that warrants further trialing, and application to other junior sporting contexts.