This research aims to disclose how the influence of different stakeholder groups is reflected in the organizational performance of nonprofit sport clubs. ANOVA, principal component analysis and correlation analysis were employed on data from 73 South-Eastern European basketball clubs. The results show that private sponsors' involvement positively correlates with the clubs' top sport achievements and financial results. In contrast, the interference of volunteers, the local community, the state and municipal authorities in club activities positively correlates with the accomplishment of local-community-oriented goals and nonfinancial objectives. The implications offer empirical support in those countries where sport clubs still operate as nonprofits for altering policy to ensure that the providers of public funds become more active in terms of monitoring the effects of their donations and sponsorships or for stimulating policymakers to think about changing the legislative framework to encourage top sport clubs to transform into profit-oriented organizations.