Purpose: This research investigated how social capital relates to physical education (PE) teachers' abilities to facilitate physical activity (PA) outside of PE class in their schools. Methods: Twenty-seven elementary PE teachers were interviewed. Data were analyzed using a multistep qualitative coding process ending in a cross-case analysis. Results: Among the three components of social capital (trustworthiness, norms, and information networks), positive norms around PE, and more broadly, PA, were most important for creating a physically active culture in schools. Trustworthiness was important, but less so than positive norms, and information networks were relatively unimportant for creating a culture of PA. Time was a limiting factor, because without it, PE teachers could not develop the social capital needed to promote PA. Conclusions: Becoming a PA leader is not just a function of will and motivation; rather, PE teachers must be supported with time and positive norms around PE and PA, which requires engagement of district and school leaders. [This paper was published in "Journal of Teaching in Physical Education" Jul 2019 (EJ1222598).]