i am pro antifa. althought i dislike the radical part of it (which apparantly is the main topic here) but radical, from any side, is bullshit.
i mean you could've made the same thread with the title "is it ok to punch an antifascist?" as this is about as common as punching nazis, or nazis punching any foreign looking people.

i hate nazi's, like literally, i hate them by heart and i show that. i have clothes that indicate i am a part of ANTIFA. (i've got a hoodie which literally says "hate fascism")
and showing that in germany(where im born and living), in cities, at some times, i can expect to get grouped up by nazi's and them punching the shit out of me just for the sake of that hoodie. infact, to friends of mine that already happened.

now i dont know where youre from/living ele to determine how bad that is there.

anyways. in those cases i certainly would try to defend myself, which is probably hopeless as they are never alone, why should they.
a part of answering to those occasions, the antifa does the same to nazis.

would i personally attack a nazi? depends on the occasion. I've luckily never been involved in such a fight yet and i rather not. but if i see a nazi attacking someone i would sure as fuck help out the other side. because fuck nazi scum.

the radical part you mentioned is pretty low compared to the amount of ANTIFA people there are not everyone is out to just punch nazis all day and those who are, are most likely idiots.