The whole slap thing was staged. Look at Smith's hand; no space between his fingers. If you're
going to slap someone there'll be a gap between your fingers. If someone is going to hit/slap you
in the face, you don't just stand there with your arms behind your back. A natural instinct is to
protect your head.
Rock made jibes at Smith's wife. Smith comes up on stage to confront him. If the whole stunt was
indeed genuine, then surely Rock would have been expecting something untoward.
* I think Chris Rock is a funny stand-up comedian.