Multilevel examinations of sport policy institutionalization are scarce in sport management scholarship. As sport policies diffuse across geographic boundaries, there is often variation in the timing of adoption. In this study, the authors used event history analysis to examine the effect of institutional factors, within and between states, on the speed of youth sport concussion legislation adoption. Our quantitative analyses show that a series of intrastate factors—state norms, disruptive events, and local advocacy—had a significant influence on the timing of state policy adoption, but interstate social networks did not. Supporting qualitative data provide additional insight about the relationship between disruptive events and local advocacy in the adoption of concussion legislation. This study contributes to a better understanding of institutional factors in the diffusion of sport policy across geographic boundaries and offers an approach for future research examining variation in sport policy or practice adoption.