Earlier quoted context omitted.
Agree. A violent reaction would be justified. It's like mugging someone with a fake gun. The victim has no way to tell whether the gun is fake or whether his life is at risk, and a violent reaction would be legitimate.
Just to clarify, a violent reaction (in self defence) might be justified. It's not automatic, and would have to be proportional. For example, it might be enough to simply grab the person and hold them down on the ground until the police arrive unless it quickly became obvious that it was just a harmless prank. If they sprayed you with something harmful, or decide to resist being detained then yes, it may be necessary…
The muscular memory kicked in and I responded to the attack ferociously. I hit him once, twice, three times (blood was splashing around), then finished him with a kick which sent a few of his teeth out. The guy was laying on the floor and yelling as if he was being skinned.
I called the police, they came and I explained them that I was attacked and that this was the effect of my defense. They dutifully noted that I was afraid, shocked, terrified, etc. and beside a round to the police station to sign off a paper I never heard about the ceases again.
I believe that that the response should be proportionate, but to the clear advantage of the victim.
Being hit once and hitting 5 times back - OK. Being slapped and responding by a kick to the body and then another one to the head - OK. Someone attacks you with a knife and you shoot him back with a gun - OK. Being attacked by a 15 yo and hitting him back as if he was an adult - OK
All these is defense against unknown and there is no reason to stop before you are safe (you do not know what that person is going to do next).
Hitting someone, he is not lying on the floor unconscious and you keep on kicking his head - not OK, there was no more risk. Someone runs away with your bag and you shoot him in the head - not OK, you were not in direct danger.
What I want to say is that the proportionality should have a 10x factor in favour of the victim.