The controversy about transgender athletes in sports does not seem to rest. Quite the contrary. The rhetoric suggests a conflict between those who advocate for inclusion and those who argue that allowing transgender athletes to compete is unfair and unsafe, particularly for women who would be ‘forced’ to compete against transgender women. One might argue that the issue of transgender athletes has become a weapon in a politically and ideologically instigated culture war. However, regardless of their position, scholars and others seem to agree that that transgender athletes are considered as outsiders in sports. Being subjected as outsiders may in fact have greater importance for how we understand gender classifications and gender ideology in sports than we first may think. In this paper, I will suggest that transgender athletes, as outsiders, constitute the gender boundaries when it comes to sports. Additionally, I will suggest that the issue is a matter of gender ideology and based on that one might claim that trying to exclude transgender athletes is not a way of protecting female athletes, as it is often claimed, but rather a way of protecting a specific gender ideology.