There’s obviously a serious, serious problem, I would not be trying to punish him by withholding a birthday present unless you just want him to withdraw further from you.
14 is still a child. He lost control. Why? What’s going on for him. This is the pragmatic question to ask if you want to repair. If you just want to be right and sod the relationship then that’s a lot easier, ignore him, withhold affection and tell him he’s a little shit via your words and deeds. I strongly get the sense that you really care about him and want to do the right thing though
Yes he needs to feel healthy shame and understand this is unacceptable, but this is such a huge overstep he has done and also you hitting him (understandably! But it is indeed likely to form part of a permanent scar in your relationship unless you are very skilful now) He’s going to need some help to get to this point
brushing it under the carpet is not a good idea. Ultimately, if I think it needs to be sorted out with professional help. CAPA first response-I go on about them constantly because they are so skilful at helping families deal with violence and a lot of it is deeply counterintuitive
A controversial comment was made earlier including that this could be the beginning of him spiralling downwards, and she is absolutely right, he should not have done it but this could be the start of a horrible chain of events, I’ve seen it and lived it myself with my own boy. If I was you, I would tell him that you love him unconditionally, you really are sorry for hitting him and you know how awful it is to loose control, and he would like to repair when he is ready because you know he is a good kid, and then try to have a serious conversation with his parents about getting some appropriate professional intervention such as referral to CAPA (they can do this themselves) or you may be able to self refer if they won’t.
I’m really sorry, you got punched, that must’ve been so distressing and shocking. good luck, stay kind and adult, be someone who helps him feel safe as this is necessary for him to truly feel remorse. Don’t bother about trying to get an apology, if it’s not a natural one, it’s not worth anything I will just make him more resentful.