Minder (1979)

Arthur Daley, a small-time conman, hires former boxer Terry McCann to be his "minder" and protect him from other small-time crooks. While Terry is putting his life at risk as he tries his hardest to satisfy his employer's demands, Arthur is busy exploiting Terry for all he is worth. When other people hire Terry's services through Arthur, Arthur usually keeps most of Terry's share of the money for himself by misleading the hard-working Terry about the amount of money he (as Terry's agent) is receiving on Terry's behalf.