This article examines a particular cultural context where transgender acceptance and inclusion are fiercely contested: women’s professional sports. More specifically, I highlight the interlocking discourses of cissexism and sexism surrounding Fallon Fox, professional mixed martial arts’ (MMA) first openly transgender male-to-female (MTF) fighter. The interplay between arguments for transgender acceptance and assumptions of fixed sexual difference circulating in MMA blogs, radio shows, and in sports and entertainment magazines, maintains barriers for Fox’s participation in the sport. I argue that regardless of the various debates for or against her inclusion in women’s professional MMA, both sides reaffirm a patriarchal, cisgender, cissexual system of power by exaggerating ‘biologically’ sanctioned male physical dominance and ‘innate’ female physical lack. As a result, Fox’s plight is fixed within a discursive paradox as the interlocking discourses of cissexism and sexism create a double bind for trans women in combat sports. Trans MTF athletes encounter cissexism on one front and sexism on the other.