What does CA stand for?
And may I ask why you would want to slap him or punish him?
CA stands for Clinton Anderson.
I guess I look at how I discipline my horses similar to how they deal with themselves. A lead mare doesn't put her arm around that little gelding and give him a firm talking to if he over steps his bounds. She pins her ears...step one. Then shakes her head...step two. Finally she lands a hoof where he doesn't want it. Step three. Enough repetitions of that and he moves when she pins her ears.
As gentle as possible and as firm as necessary. Before I started doing a lot of training I had issue with the concept of hitting your horse. A couple of things changed my mind. First, is they have a very physical way of dealing with each other. Their bodies are built to take a double back foot kick from another horse. Such a blow wouldn't hurt you or I...it would destroy us. I watched my gelding kick another (he got too close to HIS mare) gelding in the chest both hind legs...a hard Whumpf I could almost feel. Didn't hardly faze him. There is nothing that I can do with a fiberglass stick and a string to that horse that could come ANYWHERE close to that. However, I can make him think I can.
Secondly was that the concept of beating a horse is not the same as giving them a firm whack with a stick. Beatings continue long after the horse has given the right answer and continue with no reason or purpose. A firm whack says LISTEN or DON'T DO THAT. As soon as the right answer is given...back to calm *****cat. Just like the mare in the pasture. If you apply firm pressure correctly AFTER asking nicely (pinning your ears) they learn to listen to the subtle cues and respond lightly and softly. That is exactly how their mother made them listen.
Where most people go wrong is not asking gently first in a process of ask, tell, demand. A horse will only get as light as the first ask. Some horses never require an ounce of stick therapy (my gelding has NEVER been hit by the stick). My daughters horse never took me seriously and we went round and rounds of ask tell demand before he did. Now, we have his respect and he moves at the slightest suggestion...most of the time.
In the case of a horse kicking out or charging as the OPs horse did...there is no ask, tell, demand. It is NO not acceptable. Then back to calm *****cat. I often have tried to think of myself as another horse in the pasture when doing and try to think..."how would they respond?"
I am sorry this is so long and probably totally not what you were looking for but I just had a conversation like this with a friend today and it got me on a roll. I hope the OP has good luck with her horse and gets over his disrespect issues.