Saints Row 2

There are two Fight Club locations: Ultor Dome and Stilwater Prison. Do the Ultor Dome series first, since you increase your melee damage after the third and sixth fights.

Play through the Sons of Samedi missions until you unlock their fighting style, and then go to the plastic surgeon and upgrade to the new fighting style. The kick move (left trigger) is a head-high kick that can knock down multiple opponents; charge it up and let fly when enemy fighters get close.

Before starting Fight Club, stock up on $100 hamburgers from one of the fast-food places so you can replentish your health during a fight. Spectators at Fight Clubs sometimes toss food into the ring but it can be hard to reach without getting hit.

Once the fights start, stay on the outer edges of the ring and keep moving at all times. When an enemy gets close, hit them with the Samedi kick to knock them down.

If you find yourself low on health, run to a clear area and quickly eat a hamburger; whatever you do, don't let yourself get surrounded by enemies. Once again, stay on the outer edge of the ring as much as you can.

When an enemy has been knocked down you can finish them by pressing "Y" and then following the prompts; wait until their health is really low before doing this, because sometimes they can counter your finisher. The closer an enemy is to death, the less button-mashing you have to do to kill them.

Don't do all the fights at once: if you're low on food, go buy some more and then come back.

After finishing the fights at the Ultor Dome, the fights at the prison are easier because your melee attacks are now 30% more damaging. Clearing the fights at the prison also unlocks a homie that you can call on your cellphone.

Just to add to what was said by Deonaris, makes life a lot easier if you change your fighting style from the default 'Brawler' type. You unlock new fighting styles as you go through the gang missions so if your finding this hard try that!

Complete both levels of Fight Club. One is located behind the Ultor Dome, the other is located in the Prison (tiny island on the left side of the map).

Fight Club can be difficult in the higher levels, but a co-op partner should make it a breeze.

A couple things that ive found helpful... sometimes weapons will be thrown into the cage. Dont worry about pickin any of them up, instead wait for the other fighters to get them and swing at you. Position yourself behind the other fighters so that when the weapon weilding fighter swings at you they hit the other fighters instead. Also, wait before charging at a random fighter. In the higher levels two of them will fight each other while the rest come at you. I found it best to get everyones health low enough to finish them before i finish any of them, doing it this way makes the two fighters keep there attention off of you.