Regular participation in grassroot sports may benefit adolescents by developing movement skills, fostering peer relationships, and cultivating positive attitudes and behaviors. However, increased volume and intensity of sport participation raise the risk of injuries, which may lead adolescents to quit sport. Hence, sport injuries are a public health concern, yet knowledge about injury prevalence in grassroot settings remains limited. Therefore, the aim of this study was to investigate: (a) the prevalence of injury in youth grassroot football players and (b) the relationships between prevalence of injury and potential risk factors; namely, sex, age group, social support, coach and peer autonomy support, and training load. Adolescents (n = 568; M = 15.7 years; and SD = 1.4) playing for U14-U19 teams in Agder County in Norway provided information pertaining to their participation in grassroot football. Although no differences in the prevalence of injuries or substantial injuries were found between sex and age groups, the results indicated differences in injury anatomical areas based on sex and age. Moreover, the results revealed that a higher injury prevalence was associated with a combination of lower levels of peer autonomy support, higher weekly accumulated total football activity, and being female. For substantial injuries, the combination of higher amounts of match time or being a player who perceived lower levels of coach autonomy support in the group accumulating least match time was associated with a higher injury prevalence. Our results showed a surprisingly high prevalence of injury in youth grassroot football, highlighting the need for future intervention studies.