Complex sentence: His father, blaming himself for Matt's disability, stopped being an enforcer, returned to boxing, and was murdered after refusing to turn in a fixed fight for the mobster who had employed him earlier.
Split into simpler sentences: His father, blaming himself for his disability, stopped being an enforcer and went back to boxing. However, his new career was short-lived and he was murdered after refusing to turn in a fixed fight by the same mobster that had employed him earlier.