Maybe a system of positioned Offense/Defense.
In example two people are fighting, Player 1 has hit Player 2 (insert number) times in a row, therefore he's on the offense.
Since Player 2 has been taking hits and not giving them back, he's on the Defense.
As the battle goes on, the two teams (or players) constantly shift between the Offense and Defense side (different buffs and debuffs given depending on the side, etc)