if you fight you fight for self defence, ofcource. Thats the general opinion. But there are alot of people, unfortunatly, who like to fight. Either just for the hell of it, or for various other stupid reasons (you took my girl friend, for example). Though, even in most "groups" of people who do that stuff, there are moral rules one needs to follow. Where i live, there are some gangs of people who are like this (im not part of it, but everyone knows about it), but everyone of them knows that there are certain things you cant do. Id say starting a fight against a person who is not on guard by doing something like that is one of those things.