Unleashed (2005) on Netflix

Danny is the slave of British crime boss Bart, Bart adopted Danny when he was a child and has turned him into a dog and makes him wear a collar around his neck. When Bart removes the collar from Danny's neck, Danny unleashes his lethal fighting skills and becomes a killing machine, when Bart orders Danny to attack the targets. After being wounded in a accident and Bart ends up in a coma, Danny is befriend by a American blind piano turner named Sam and his teenage stepdaughter Victoria and they welcome him into their family. Sam and Victoria decide to teach Danny about the world and being human. When Bart wakes up from his coma and he and his gangster want Danny back and forces him to take part in an illegal gladiatorial fight club to earn money, Danny decides he doesn't want to hurt people anymore and sets out to protect Sam and Victoria and fight for his freedom.