Showdown (1993) on Netflix

Billy Grant (Billy Blanks) is a police officer who is called to stop a noise complaint at a local party. Along with his partner, Spinelli ( Michael Genovese), Billy enters the house to find two men causing all sorts of trouble. When Billy attempts to stop things peacefully, one of the thugs attempts to assault Billy, who uses his unarmed combat skills to stop the thug. However, when he puts the thug down, the thug's head smacks hard against the stairs. The other troublemaker looks in horror and yells to Billy, "You killed my brother, pig!". Spinelli shows up and arrests the one thug. Billy attempts to revive the thug's brother but he ends up dead. Feeling guilt for what has happened, Billy decides to quit the police force.