I think the word you're looking for is "vendetta", or "revenge", and generally isn't considered a valid legal defense for violence. If I find out that someone

I think the word you're looking for is "vendetta", or "revenge", and generally isn't considered a valid legal defense for violence. If I find out that someone punched my kid, I'm not allowed to drive to their house with a baseball bat and hit them with it. If I happen to be carrying a bat, and someone starts punching me, I'm _probably_ allowed to use it for defense ... but I am not a lawyer and there are many nuances there as well. :)