When the woman got out of the car and ran away, police said Coleman followed her and continued to fire shots.
The bystander, a resident of Pegram Street, heard the shooting and intervened, police said.
"He challenged the individual with the gun, and the suspect did not put down the gun, and the homeowner shot (him)" said Lt. Luke Sell.
Coleman and his grandmother were both taken to Carolinas Medical Center, where Coleman died. The grandmother was expected to recover.
Police have not identified the grandmother or the bystander. Homicide detectives were canvassing the neighborhood for further witnesses.