I believe that happens because the way the character falls and because of the type of weapon the character has. And there isn't a way to switch styles backwards.

Yeah, I have wondered about that for a while.
But I think it's to do with the different getting up animations. For example the one where they bang their hands on the floor can't be done with weapons? Or something.

I think it's to do with the way they were knocked down at the end of the round.