To explore the relationship between social support and adolescent athlete engagement and the role of self-efficacy and mental toughness in this relationship. Participants and methods: This study was a cross-sectional study. Convenience sampling method was used, and adolescent athletes from seven youth sports schools in China were used as subjects. Five hundred and thirteen valid questionnaires were recovered, 264 (51.46%) males and 249 (48.54%) females, and the mean age of the athletes was 17.8 ± 1.1 years. (1) After controlling for the effects of adolescent athlete age and sport level, regression analyses revealed that social support positively predicted adolescent athlete engagement
(2) Self-efficacy and mental toughness mediated the relationship between social support and adolescent athlete engagement, and this mediation consisted of three pathways: parallel mediation of both self-efficacy and mental toughness, and chain mediation of both self-efficacy and mental toughness. Conclusion: The mediating effects model constructed in this study can inform the promotion of youth athlete engagement levels, which can be crucial for improving youth athlete engagement in the future by enriching youth athletes' social support networks, enhancing self-efficacy, and developing mental toughness levels.