This essay focuses on the relation between amateur sport and Union citizenship, analysing the recent Biffi ruling of the European Court of Justice. It examines the opinion of the Advocate General and the Judgment of the ECJ, starting from the established case-law according to which sport is subject to EU law insofar as it constitutes an economic activity. Taking into account the possible application of the Treaty in light of the indirect impact on economic activities of the amateur athlete, the study analyses the legal implications of Article 165 TFUE considering the social function of sport. Finally, the paper illustrates to what extent the Biffi case represents a simple clarification of the existing legal relationship, a coherent case-law development, or another seismic ECJ ruling on sport.