ABSTRACT Research question This study investigates the impact of fantasy sport on online sport fan identities. It explores the socio-psychological outcomes experienced by sport fans participating in fantasy sport and investigates their collaborative value co-creation practices. Research methods We use netnography to collect user comments across relevant subreddits. We further employ content analysis to identify the socio-psychological outcomes experienced by sport fans participating in fantasy sport and to gain insights into value co-creation practices within the fantasy sport community. Findings This study presents three significant findings. Firstly, it delineates BIRGing as celebration and trash talk and CORFing as disappointment, contemplation, and avoidance. Secondly, it introduces two new socio-psychological outcomes – FAGing and FARDing – encapsulating the dual identity of sport fans participating in fantasy sport. Third, it identifies three unique co-creation practices observed in fantasy sport communities – favoritism and subgrouping; sharing, supporting, and strategizing; and bragging. Implications This study contributes to our understanding of the impact of fantasy sport on the fan – team dynamic and the emergence of distinctive co-creation practices among evolved fans. From a practical perspective, the research has implications for sport managers and fantasy sport platforms, as fantasy sport serves as a powerful tool for engaging audiences of professional sport leagues.