Yeah, that's what I have a problem with.
There are rules to war and to fighting.
That guy has his hands up in, not a defenesive fighting position, but in a defensive I don't want to fight position. See how he holds his open hands like he's not trying to fight?
Then he throws a sucker punch to knock the dude out. Now, the dude's posture was still in a fighting mode (although a bad one because he's leaning forward, chin out, and hands down) and we can't hear what could have been said, but throwing that punch looks dirty to me.
It's like that Mexican way of fighting where they slowly walk up hunched over not looking like a fight, then just start throwing.
Look at the video, he stands there, hands wide open, in a "calm down mode" right before throwing the punch.
That's wrong and he should get his ass beat for it.