While the benefits of sports activity are well-documented, people remain reluctant to engage in it in selected developed countries (including Middle and Eastern Europe). A comparison of empirical results indicates that the reasons behind such behaviour are heterogenous and complex. As implied by the socio-ecological framework, different spheres of life and the interactions between them matter. By using the results of a study on Polish society conducted in 2015, Social Diagnosis, and a random forest model, we show the key demographic, socio-economic characteristics and interactions between them in explaining the difference between engaging in sports activity and not doing so. In particular, we identify three crucial variables: age, participation of other adults in the same household in sports activity, and proclivity for restaurants, bars, pubs.