The reemergence of roller derby as a sport ‘by women, for women’ has brought with it great hope. As a fast, aggressive, contact sport there is the potential for women to challenge gender norms of passive heterosexuality and spectatorship. Played mostly by women, yet officiated mostly by men since its reinvention in the early 2000s, issues of gender are central to all aspects of the sport, including its governance and management. Yet currently, the role of men in roller derby – as referees, coaches, and players – is unexplored. While the common conception of derby is that it inverts the gendered sporting dynamic – women playing and men in support roles, the reality is a complex interplay. This article examines the rise of mixed-sex/gender roller derby leagues and what this means for both the experience of participants, and the future of the sport more broadly. Drawing on ethnographic approaches to the study of sport and physical culture, the article provides detailed accounts of current points of tension in roller derby as they relate to sex integration/differentiation. Perspectives from players and officials, both in Australia and the US, are explored to illuminate the varied ways sport and gender can be thought about, governed and experienced as roller derby continues to gain popularity around the globe. The gendered tension in derby mirrors wider arguments within feminist movements about the role of various genders in ‘women’s’ spaces and movements. Consequently we offer an empirical exploration of the lived experiences of this discourse within a sporting context.