This dissertation uses a mixed-methods approach to examine the conditions that enable opposition to transwomen participating in women’s athletics. I draw upon interviews that I conducted with eleven transwomen athletes who train and compete in various sports; participant-observation at lesbian, gay, bisexual, and transgender sporting events; autoethnography of my experience as a gender non-conforming athlete; and discourse analysis of cultural representations of trans athletes in news outlets, social media, trans-exclusionary groups. This project is one entry point to bring sport within the scope of trans studies and seeks to model a closer conversation between feminist sports studies and trans studies, or what I call transfeminist sports studies.