I'm not hippy dippy over here, just applying empathy and learning to time-outs. Instead of punishments for bad actions they are a chance for him to communicate what's wrong and a chance to teach him how to handle his emotions. It is a long ass road for sure, and I certain don't leave him to handle physical situations himself. It is only occasionally he gets upset about something and notices he needs to calm himself down. Most of the time, he needs guidance.
His preschool is actually where most of these techniques come from and they spend a bunch of time identifying feelings and keeping things positive/productive and do things like have the kids jump on a mini-trampoline to burn off excess energy.
If he is hitting someone, I immediately move him away and try to work him through talking/breathing/etc. Most really bad situations can be avoided by putting him in a position to succeed. That just means stuff like don't keep him out until 11pm and don't drag him around unhappily if we can help it. He is only 4 but we try to respect his personhood - he doesn't make the rules but we consider his wants/dislikes and warn him when we know he is going to need to do something he won't like. In turn, he tends to behave better in those situations - he has been on a 13 hour flight with no drama. In his life, has only required a kicking/screaming drag away response maybe once or twice. A lot of that is simply avoiding those situations before they develop.
All kids push boundaries so we try not to set fake goalposts, (i.e. No cake for you if you do this! But then give him the cake anyway.) We only threaten things we are willing to go through with, even if they mean shittiness for everyone. We've left stores before we wanted to, left dinners early and left parties early to avoid meltdowns. While it sucks, those are big events that prove we aren't making empty threats but informing him of real boundaries. When we know we can't uphold something we simply don't threaten it.
He also has a younger brother (2 yrs) and of course they fight over toys often. The progression goes from: "Did you ask or just grab? Can you share/take turns?" If the younger one is grabbing from him (which is more common): "Can you trade/offer him an alternative toy? Can you ask him to wait instead of fighting for it?" If none of that works, I take the toy away for a while and say "that's the rule". It's great to blame the "rules" because they can't argue against them.