Most pro punchkickers keep their hands or guard near their face for obvious reason. The closest this crab stance comes to is a warped cross arm block or abstract Philly shell, which was favoured by Foreman and Mayweather respectively. I was never fit enough to stick with Philly shell when I tried it and switching back to normal stance pretty much tells your sparring partner “I’m tired now :(.” TIL crab defence is actually what they’re called lmao.

Edit: to answer your questions, no formal fight training and learning to fight from tv and internet fight clips.