Ring Of Death (2008)

Ex-cop Burke Wyatt (Johnny Messner, "The O.C.") has one chance to get his life together, but this assignment might be his last. Wyatt is sent deep undercover into brutal Cainesville State Prison to investigate a string of bizarre prisoner murders. Once inside he discovers the truth: a fight ring in which the inmates are forced to fight to the death. With no way out, Wyatt must survive "the cage" or be sent six feet under.

See:
# Ring of Death (2008 film) at Wikipedia