A "hero" motorist who pulled over to break up a fight was hit and killed by a car while his three children watched nearby.
Police said one of the men arguing was disabled, and Kevin O'Connell intervened to help someone he thought was being victimised.
One of the two men ran away, so Mr O'Connell chased him.
He was then hit by a car in Burton Road, Derby, at about 12:55 BST on Saturday.
The 33-year-old later died from his injuries. His children are assisting police with their investigation.
'Sense of duty'
Sgt Darren Muggleton said: "It's a tragic incident which was witnessed by Kevin's three children.
"He died a hero trying to help a member of the public he thought was being victimised."
Police believe Mr O'Connell initially saw part of the altercation as he was leaving a chip shop with his children.
Sgt Muggleton said: "He must have found a sense of duty and he decided to drive down the street and intervene in what was happening.
"We believe that there has been some heated discussion, other things have occurred, and as a result one of the males has run off from the scene and he was pursued by Mr O'Connell.
"At some point Mr O'Connell has somehow stumbled into the path of an unconnected passing car, causing him his fatal injuries."
Police said the altercation was on the footpath at the side of the road, near Car Parts Direct.
Two men, aged 27 and 34, were arrested on suspicion of assault and bailed.