Sport clubs are considered an ideal setting for the social integration of people with a migration background. However, they can also be a place of social closure practices, where assimilative ideas and ethnic boundaries are present. Besides the individual characteristics of the members, adequate club organizational structures are relevant for preventing social closure and facilitating social integration. Thus, the role of organizational structures for social integration might differ between natives and people with a migration background. Based on data from 42 Swiss sport clubs and 780 sport club members, with and without a migration background, we analyzed individual (migration background and membership biography) and structural factors (situational, club goals, and club culture) using multilevel models and tested cross-level interactions between structural variables and migration background. The results reveal that membership biography (e.g. membership duration and volunteering) and migration background are relevant for social integration. The estimated cross-level effects reveal that, unlike for natives and second-generation people with a migration background, structural conditions are especially relevant for first-generation people with a migration background. For example, social integration increases with a higher proportion of people with a migration background in the club or a less assimilative club culture.