In popular and professional discourses about effeminacy or sissyness, boys’ feelings about sport and their actual athletic abilities have been represented both as symptoms of gender deviance and as targets for clinical intervention. The assumption has been that knowing something about a boy’s feelings for sport tells us considerably more than that about him. This article looks at the special role played by sport in what Eve Kosofsky Sedgwick once called “the war on effeminate boys” (1991). Following Sedgwick, the article considers how gendered ideas about sport and athleticism came to influence the diagnostic criteria that made up the highly contested diagnosis of Gender Identity Disorder in Childhood (GIDC) that appeared in the third (1980) and fourth (1994) editions of the Diagnostic and Statistical Manual of the American Psychiatric Association. The article analyzes the specific behavioral criteria that came to ground the diagnosis of GIDC, showing the effects of sport discourses well beyond the playing field or the gym. Sources are drawn from two overlapping literatures: early and mid-twentieth-century psychological studies that focused on sex differences in children’s play; and a small specialist literature, written by psychologists and psychiatrists, beginning in the early 1960s, on the “problem” of effeminate boys. My reading of these texts considers how they were informed by gendered discourses around sport and play behaviors; I pay particular attention to scales and other instruments developed by researchers and clinicians to measure “gender abnormality” in boys’ play. I argue that effeminate boys—and other queer people—need a physical culture that helps shift, rather than reinforce, understandings of the body and gender; that challenges the links between bodies, genders, and sexualities; and that traffics in uncertainties about who can and should do what with their bodies. Mainstream sport is not yet that thing.