Best defense system is to attack first, take the opponent by the surprise, everything is allowed. From the experience- man who gives first punch is usually winner.
Yea, even one step before is not letting yourself in situation when you gonna need to fight, just avoid. It is cheaper not to fight, in normal times it can cost you money and lawyers, in SHTF time it can cost you life.
Every fight is gonna hurt you, even the fight where you win fast will leave some “marks” on you, just avoid if you can.
If not then use every dirty trick to finish the guy fast, use advantage of any weapon, forget the “fair” fights, real world is not school yard.