This is the Westeros equivalent of letting the team mascots battle to the death. Think of the savings!
Whether you are Team Greyjoy, Stark, Baratheon, Targaryen, Lannister, Mallister, or Tully, you can enjoy a visit to the Mega Bowl of Death. Just send your hawk, lion, dragon(s), stag, direwolf, octo-squid(?), or dead fish into the ring and sit back while the royalties get transferred directly to your shirt. Consider the stats...
HAWK - flies, has talons, is bird
LION - loud, awesome mane, sharp claws, biggest possible cat
DRAGONS - they're dragons
STAG - antlers, has party named after it
DIREWOLF - hell dog, sounds even cooler than wolf (and wolf is really cool)
OCTO-SQUID - lots of arms, underwater breathing
DEAD FISH - offensive smell
So place your gold coin bets and let's watch these animals hurt each other on a shirt until the Westeros version of PETA shuts down the operation. It's ok, we'll just move the fight to another shirt.