@1-800-GRINGOD | Honestly, I'm not sure if Chris Rock knew about Jada's condition. He might've just thought she was shaving her head and made a harmless joke about it, unaware of her alopecia. If he did know, it was uncalled for and the slap was well-deserved. But if he wasn't aware, then I can understand.
Personally, I don't think Will should've done what he did. If he didn't like the joke or wanted to defend Jada, then he should've dealt with it afterwards without the use of physical violence. However, Will defending his wife is an honourable thing and I wouldn't expect anything less; just should've been handled more maturely.