Closed-fist punching is never okay on a child. Period. End of story.
By child I mean under the age that can kick my ass of course.
Were my son to be 17 and thinking he could get away with doing something just because he was "grown" there may be times I might lay the smack down. Never a fistfight though.
But, those that say physical punishment of any kind is never okay.. Well, you're idiots. That's why you have all the little monsters running around these days, that don't respect anyone and exist solely to cause trouble.
Yes, I have a son. He's almost 2. So he's extremely curious, and at the age where he KNOWS he's doing something wrong. For normal things like making a mess, etc. Just a saying no and then if it continues giving him a "time out" on the chair for a couple minutes works fine.
But. For things he does that are dangerous to his health and well-being (i.e. playing with an electrical socket) he gets told no, and if it continues immediately after that, he gets his hand slapped and then sat down in a time out.
Surprise. The small amount of physical punishment is like night and day vs. just the "time out" and talking to. Rarely do you see him going back to the dangerous behavior in the same day or so. Kids his age do have very short memories though, so one in a while a reminder might be necessary.
I don't think I'll ever go all-out and spank him when he gets older, as he's a fairly well behaved kid. But if I had a little terror that hurt people and didn't listen, I sure wouldn't leave it out of consideration if all else failed.
I was spanked as a kid, probably too severely so I'm not going to make the same mistake. But, I turned out fine, and as a kid and teenager actually respected people.
All that said, physical punishment of any kind out of anger is a VERY large "no". Period.
-Phil