L.A. Heat - Season 1 Episode 12 : Old Scores 1999

A promising young boxer is beaten and left nearly dead. Arriving at the hospital, August and Chase intercept a hitman who attempts to finish the kid off with a lethal injection. They pursue the would-be killer through the hospital, finally stopping him with a jolt from a set of defribulator pads. Immediately, they sense that this case involves more than a random beating. August is visited by his former boxing coach, Frank, to whom he hasn't spoken since their falling out many years before. Frank says that he must tell August a secret that has been haunting him. But before he can reveal what he knows, Frank turns up dead, plunging the detectives further into mystery.