To complete this fight you will need to defeat 12 enemies initially. More will come into the arena once 8-10 of the enemies have been knocked out. To win this fight you will need to get a combo together by dodging the incoming attacks and dealing out punches of your own.
Go towards the direction of an enemy and strike them, immediately after striking change direction towards another enemy. Continue to do this to get a combo going. Once you have your combo going, keep it up by bouncing to different enemies and hitting them. Be sure not to get hit by moving towards enemies that are outside of the pack. By aiming at these enemies first you will be able to get your combo up without getting hit.
Continue to do this. If your combo gets interrupted dodge enemies and build up a combo again.