Danny the Dog (2005) AKA Unleashed

This is the story of Danny, a slave who has lived his whole life without any sort of normal human education, with the mind and personality of a young child, with only one lesson learned: how to fight. Treated like a dog by his owner/boss, Bart which includes having to wear a collar. Danny has been raised to be a lethal fighting machine who fights to help Bart extort people and later ends up in illegal gladiator-style fight clubs, where he earns lots of money for Bart as the undisputed champion. After a car accident that lands Bart in a coma, however, Danny meets a kind elderly blind piano tuner, who uses music to teach Danny some things about the world and about being human.