Fight Fair, fighting fair, give him a fair fight, etc. We’ve all heard it before. Here’s what it’s likely intended to mean, or at the very least, SHOULD be taken to mean:
1. In a sanctioned, competitive fight, (boxing match, mma competition) one ought to abide by the rules of the competition.
2. In a street fight, if one is attacked by another intending to do them harm, one ought to respond with proportionate force. (Eg, if someone drunkenly shoves you and starts to walk away, you ought not shoot them in the back, or maybe this.)
These seem like common sense, but I’ll go into a bit of detail in a minute. First, it’s important to point out what this idiom could be, and perhaps sometimes is taken to mean:
1. In a street fight, if one is attacked by another intending to do them serious bodily harm (kill them, rape them, stab/cut them) one ought not to do things like bite, spit, pull hair, or hit the groin, because these types of attacks are rude.
Now, I really shouldn’t have to spell it out since that’s basically written in parody, but I will anyway. If someone is seriously trying to hurt you, you need to think about what you’re willing to do. Is “not spitting at someone because it’s rude” more important than living? I’m pretty sure the answer ought to be a resounding No, it’s not. There’s no such thing as a fair fight when one person is attacked by another. Always do whatever it takes to stay alive, as long as it doesn’t break #2 of what the idiom might be suggesting. Think, be cautious, don’t over react, but also don’t hold back if someone threatens your life.
As far as I’m concerned, this is something that should be made a point of in all basic self defense classes.