To what extent is reciprocation (of harm) allowed in Islam?

If a man had the guts to hit you in the first place when you had done nothing wrong then I think if you slap him too he will go the extra mile and more fitnah will come. I think the most important thing is to make sure there is no fitnah, if that means the best way will be to hit him back then you can do that but I say don’t, just report to the authorities and they will deal with it in sha Allah. But if you have to then you should not respond with more harm, but the same harm he had caused you and this is not always the best solution (reciprocating harm) as it will cause more fitnah. The Prophet is reported to have said:

“There is to be no causing harm nor is there to be nor is there to be reciprocating harm” [1]