IMPORTANT: the only way to get this achievement is to unlock Overtime mode. To do that, after TK is bit by a zombie, you'll need to give him some Zombrex (Yeah, after all the trouble he's put you through in the game, the last thing you want to do is give him Zombrex, especially since you need it more than him). Just give him one dose, and then go finish the Case Files up through "the Facts." After beating a HUGE boss fight, you'll see a cutscene or two, watch the end credits role, save your game, and then...
TK shows how grateful he is to you for giving him Zombrex by kidnapping one of the leading female characters and making you run around for several objects (There are 6 total, and they're scattered throughout the maps). Once you get them all, go back to the arena. Make sure you go in at full health, and don't worry about making your favorite weapons - you'll lose everything when you enter the arena.
Phase 1 - After TK gets the drop on you and knocks you out, you wake up back where the game started - the zombie arena for TIR. Your goal is survival, and grab everything you can get your hands on (Food and weapons). Zombies will come at you, but not in droves, and you can use the ring's traps to help take care of the zombies. If you hold out long enough, a cutscene will occur and you'll move on to the rafters above the arena.
Phase 2 - you have 2 objectives: Keeping the hostage alive so she doesn't bleed to death, and beating TK. Word of caution, he is CHEAP! You'll be lucky if you get away from him to heal yourself. His attacks range from swinging his microphone to charging you and then beating on you. If he charges you and starts beating on you, you'll have to wiggle the left thumbstick, then do two random button-presses to knock TK off you. Occasionally, TK will run away and hide: it's good because it gives you time to heal some and to heal the hostage, and it's bad because when he comes back, he'll let you have it with eiethr a charge attack or (if you're healing the hostage) knock you aside and start pounding on you.
My advise is to hit him once and then get away before he can hit you. If he starts to charge, dodge him quickly. When he goes off and hides, heal yourslef and the hostage a little, then get ready for TK to come back.
I fought him at level 45, and I was down to one bar of health, hardly any food, when I had TK about 4 hits away from beating him; I went at him and somehow managed to beat him, but I was expecting to lose (for the 2nd time, too). Be prepared to lose - make a save in the bathroom near the Arena entrance at the Americana Casino.
Note: if you die and reload from your last checkpoint, it will be as you enter the arena's entrance. That means you will have to do the ENTIRE fight from the beginning.