Many a drunken brawler has been arrested for fighting. If only he had known to discuss the fight with his opponent beforehand, he could have escaped jail time. Mutual combat is a legal term and is defined as "a fight into which both parties enter willingly, or in which two persons, upon a sudden quarrel, and in hot blood, mutually fight upon equal terms."
Back in the day, this type of fight was much more common. There were formal duels between men. School boys were made to fight as a rite of passage. Today, the boxing ring and other formalized (often for entertainment value) forms of fighting are the only places where mutual combat exists.
According to most, mutual combat has not survived the common law and would no longer hold up as a defense. However, it is still part of the criminal law of the United States.