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if you respond for self defense because otherwise that person would keep striking you, you have the right to respond. If that person strikes you one time and then walk away, you don't need to exercise any violence but you should call the police or the institutions to legally protest and ask for defense against the violence that has been used against you.

So the whole "if they turn their back to you, your hands are tied" schtick? No. Doesn't work that way. Ethically, once someone violates your body through force, you are ethically excused from liability for responding in kind.

I'm not going to delve to deeply into it, but this is a philosophical discussion. You have the ethical right to defend yourself against an attacker, even if they hold their hands up immediately after attacking you. The police or other "legal" institutions in place that claim dominion over the provision of security don't change that.

I agree and the reason for this is that it prevents future violence and is not just vengeance. If someone hits you and then sticks their hands up so you don't do anything then they got away with it and will likely do things like this again.