Rugby, like football, is largely a game of agility. I doubt very much an 18st man would ever condescend to join a team of ladies. There is a taboo against men appearing to be 'cissy'.
Few men would ever dream of presenting as female in any way. My ex- would fret if his t-shirt was too long as he didn't want anyone to think he was wearing 'a skirt'.
That is the kind of toxic masculinity/femininity that I suspect of playing a role in gender dysphoria.
I had a girlfriend who objected to my pink sleeveless shirt, the kind that is often called a wife beater, because people (!) might not find it sufficiently masculine.
Remember the mutually assured humiliation of Homer Simpson and Ned Flanders?
