Background Although outdoor smoke-free policies (SFPs) at sports clubs represent an important new area of tobacco control, the majority of sports clubs are not smoke free. This study aims to assess diffusion patterns of outdoor SFPs at sports clubs in the Netherlands. Methods Using a retrospective, registry-based design, an inventory was made of football, field hockey, tennis and korfball clubs that became smoke free between 2016 and 2020. We determined the type of sports, number of members and proportion of youth members. The degree of urbanisation and density of smoke-free sports clubs were measured at the municipality level. The association between sports clubs’ characteristics, degree of urbanisation and SFP adoption was analysed using multilevel regression analysis. Horizontal diffusion was tested by analysing the association between the density and annual incidence of smoke-free sports clubs. Results Since 2016, the number of sports clubs with an outdoor SFP increased from 0.3% to 26.4%. Field hockey and korfball clubs and clubs with many (youth) members were more likely to be smoke-free. SFPs spread from the most urbanised to less urbanised municipalities, which could mostly be attributed to sports clubs’ characteristics. A higher density of smoke-free sports clubs within municipalities was associated with an increased incidence of new SFPs in the following year. Conclusion Outdoor SFPs at sports clubs in the Netherlands diffused across horizontal and hierarchical lines. National strategies for smoke-free sports should monitor clubs that are more likely to stay behind, such as football and tennis clubs, smaller clubs and clubs in less urbanised areas.