Abstract: In the context of the "Sports Powerhouse" strategy, there is an urgent need for developing new theoretical perspectives and intervention pathways to enhance adolescents' physical fitness. This study adopts a theory-driven empirical research paradigm and is grounded in the localized context of China's class-based school system. We construct the concept of "class-level sport social capital" through two dimensions—"network embedding" and "resource attainment"—and categorize adolescents to four ideal-types based on the level of capital stock: dual-advantage, resource-advantage, structural-advantage, and dual-disadvantage. Empirical results from the China Education Panel Survey (CEPS) reveal that both the degree of class network embeddedness and the level of class sport resources exert significant positive effects on individual physical exercise behavior. These factors also exhibit a synergistic effect, leading to structural differences in physical exercise levels across distinct adolescent groups. Policy implications: Schools should establish classes as core intervention units, prioritize cultivating class-level sport social capital, and implement tiered, targeted interventions tailored to different youth groups. This approach will effectively enhance adolescents' sport participation and contribute to building China as a sport powerhouse.