This explorative study examines whether the involvement of different stakeholders in South-East European basketball team activities significantly correlates with two crucial constructs often reported to be predictors of well-functioning teams in interacting sports, namely trust and cohesion among team members, and discusses what might cause these relationships. The Group Environment Questionnaire and a four-dimensional “competence-benevolence-integrity-predictability” trust scale were used for a sample of 73 basketball clubs from South-Eastern Europe (559 athletes, 73 head coaches, 73 directors). Correlation analyses showed that team cohesion is in a negative relationship with the influence of media, while trust within teams positively correlates with the influence of professional athletes in team activities. The trust relationship between athletes and coach is weaker in the case of private sponsors’ interference, while the coach's trust in the athletes positively correlates with the influence of volunteers. These findings combined with the literature review show that in the context of post-transitional South-East European sport clubs’ higher level of professionalisation appears to make it easier to achieve trustworthy relationships and higher team cohesion, while an increase in private sponsors’ interference might impair the coach–athletes relationship. The study provides a robust quantitative starting point and a set of new research questions for further examination of the causality between stakeholder activities and sport team dynamics, whereas from a practical point of view it points to relationships in need of greater attention in the stakeholder management process.