Defeat the Warmaul Champion. Should you win, speak with Wodin the Troll-Servant to collect your reward.
They had to ship the champion in from the Blade's Edge gladiator pits. He was training on mountain giants - three at a time.
If you win this one, you become the new champion. What do you think your odds are, kid? Do you have a shot? Just give me the word and I'll bet the house on you.
Now get in there and win!