Cheers to you for asking for some help! Went throught the same thing with my boy.
I have some suggestions for you; I know this might be hard but, 1.Apologise profusely for hitting him and dont ever do it again. 2. Share your genuine concerns, fears, and feelings from your heart. No drama, psycho-therapeutic babble, just tell him what your actually feeling. (Touch base with your self first; What is it, really, thats driving you to such rage as to physically harm him)?
3. Now this one is gonna sound really crazy; but help or facilitate him to take some healthy risks. Buy him a used motocross bike and take him out to some backroads. give 'em his board back and take him to a skate park, or get him out on a kayak, bungee jumping, etc., etc. he is going to be taking risks anyway, help steer him to some good ones. Most importantly tell him no matter what he does, you will allways love him and tell him this every single day. especially when your feeling as angry as you descirbed earlier. You will be amazed how saying those words will de-escalate you and put you back in control and in tune to what your really afraid of. Do one nice thing for him every day because he is your son.
he will probably initially make you "prove to him that you love him" by treating you like ****** and sabotoging your love, but dont give in.
You are NOT going to Make him do anything. I can gaurantee you that. You got some work to do to get back some trust. hang in there, and be there.