I don't have hard sources, could probably find relevant ones if I reeeallly had to. What's interesting isn't sports' exclusion of trans people, rather the supposed eligibility threshold resting on having never undergone natal puberty, juxtaposed against scare campaigns around targeting children, along with the already significant hurdles faced in accessing treatment prior to pubescence anyway.
sport: no trans athletes that haven't undergone hrt before the age of 14
law: no trans kids can undergo hrt before 16
perfect system
It's also just another method of exclusion and its supporters know it