I've never trapped ferals with injuries, so I don't know what protocol is there, but you might need to take the feral "home" with you after treatment and keep it in the trap in a safe place (like a garage or bathroom). You'll need to release the feral where it came from afterwards.

forgot to clarify that when you take the feral "home" with you, you keep it in its trap.

This one won’t get to keep its leg, so I think it can’t be rereleased. If it’s actually feral I think euthanasia might be more humane because I can’t imagine doing effective wound care on a cat stressed to 11. But I’m hoping it’s just a long-term stray! 🤞🏼

Yeah, I kept my last two mamas for a week after their spays. They were NOT happy about this! I, er, did let them out in their bathroom (see above re: they knew me, DO NOT RECOMMEND) and gave them carriers to hide in. To release, I shut the carrier doors for the first time and carried them out.