It might help you to understand that there has been a lot of study in many sports (for the very reason of your uncertainty).

Apparently, testosterone level (not birth gender) is the effective indicator of expected performance. In all women's sports that allow trans competitors, trans individuals need to test **lower ** testosterone levels than are naturally allowable in cis women.

The issue is this. For someone trans to be willing and able to power through all the bullshit, they need to be uniquely dedicated and talented (or they'd just not do it). What that means is that unsurprisingly some trans individuals are absolutely phenomenal at a given sport.

Ultimately, there's the problem. "We" seem to think a m>f individual doesn't have an unfair advantage ONLY if they lose. So we're not looking for the average or variance of skill, only the fact that there exists a trans individual that shines. It's hard not to look at a trans woman winning and say "see, that's what happens when someone born male competes with a woman in this sport". But it's also unscientific, as the science says trans women compete with comparative attributes to cis women.

Chess? Banning trans competitors is fucking idiotic and the chess federation can fuck right off with that implied notion of women being less capable.

Yeah, there's no real defense to the two being separated in any league.