Participation in sport is associated with a number of physical, social and mental health-related benefits therefore designing programs to increase participation is crucial. Modified sport programs promote involvement by ensuring the environment is safe, inclusive, team oriented, and age appropriate for the development of sport knowledge and skills which facilitates sustained involvement in sport. The Australian Football League (AFL) Junior Football Match Guide is a modified program for junior competition in Australian Rules Football for participants aged 8–12 years. This research evaluated the impact of the AFL Junior Match Guide modified rules program on player participation (through involvement in play) and psychosocial measures of perceptions of enjoyment, competence and competition and winning.