I'm in the it's real camp, as Chris Rock's reaction didn't look fake at all. It's either he expected a punch but got either surprised by how weak/strong it was.
He has Will Smith approaching him with a death-stare, he's obviously going to clench up and assume he's about to get slapped. The slap did look weak, there was a lot of "kayfabe" movie movement in Smith's body and I think the connection was more palm to lower cheek/chin, but I think Chris might still have found it too strong for something that's happening to you on live TV in front of the whole world. Afterwards he does get a bit flustered, defends his joke at first ("It was a G.I Jane joke, man...") and then proceeds to smile and say he could roast further, but chose not to. Not to mention he says to Jada "I love you" before making the joke and he then compares her to a fucking empowered soldier woman from a military film that happens to have a buzzcut. Let the troons freak out about ableism all they want.
That's a really, really bad look for Smith and I don't think it was staged, but even if it was, Chris Rock didn't seem to be in on it. If I was Chris Rock I would also not press charges, since the crazy more famous nigger that slapped me can defend his bald wife as much as he wants, but he can't uncuck himself or fix his marriage. Let him enjoy his Oscar, I say.