Recently, a story has been making the rounds of the usual news outlets about Mack Beggs, a teenager in Texas who won the female state wrestling championship. Generally not national news, but in this case Beggs was born female and is transitioning to male.
That rule about competing as the gender on your birth certificate sounds familiar - it's similar to the North Carolina Bathroom Bill that caused such an uproar last year. But I think there's a significant difference here. There's no competition involved in using a bathroom, but in sport the competition is the main focus. While I see the bathroom question as a discrimination issue, I think in sport the issue is about maintaining a level playing field for the other participants.
If anyone else took a performance-enhancing drug while participating in competitive sports, the rules would prohibit them from competing. (Or at least put them in a more appropriate category, if one exists. In this case there's probably not enough born-female-but-testosterone-enhanced participants to have such a category.) It seems to me that the only reason we're even hearing about this issue is that the drug was taken as part of a gender transition.
I don't have any problem with someone making a life choice that is appropriate for them (even if I don't understand it, which in this case I certainly don't). But I also think we need to recognize that every life choice that a person makes opens some doors and closes others. No choice should cause discrimination, but it also should not infringe on the rights of others. In this case, the right to compete fairly against other similar participants. We all make choices on a regular basis that affect our opportunities, and while this one is a bigger decision than most, it shouldn't be treated any differently.
When Beggs chose to take testosterone, that should have closed the door to participation in competitive wrestling (and likely, any other sport). The reason for taking it shouldn't matter, only that it was a free choice made by the athlete which caused an competitive imbalance.