Police said Eric Hood, 54, jumped into a running car parked outside a pizza shop around 9 p.m., WCAU reported.
A 25-year-old woman had left her three young children, who are between 7 months and 5 years old, in the vehicle while she went inside to visit her boyfriend, who is the father of two of the children and works at the restaurant, WCAU reported.
The woman's boyfriend ran after Hood, who drove about half a block before the car was stopped in traffic, WPVI reported.
The man removed Hood from the vehicle and proceeded to severely beat him while bystanders joined in, WCAU reported.
Hood was unconscious and had severe injuries to his head and face, WCAU reported. He was taken to a hospital, where he was pronounced dead.
The woman and her boyfriend were questioned but have not been charged.
Investigators are waiting for a toxicology report to determine an official cause of death and if Hood had drugs in his system, WPVI reported. Police said Hood has 24 previous arrests and convictions, WCAU reported.
The children were not injured.