In the first part of this paper, the authors analyse definitions of the term sport and its use within Croatian legal acts regarding sports (the Croatian Sports Act and bylaws of the Croatian Olympic Committee), as well as several international legal acts (especially those of the International Olympic Committee - IOC) on which the Croatian acts are based. The analysis shows that these acts do not clearly or precisely define the term sport. Thus, in the second part of the paper, the authors turn to the philosophy of sport research literature and its definitions of sport in order to find solutions for the sports law. In the third part of the paper, the authors present their interdisciplinary proposal – integrating four determinants of sport into a sport legal system, especially for the purpose of deciding whether a particular human activity should receive the legal status of a sport.