It happened around 1:00 p.m. in the area of Wayne and Rowan avenues in the Tioga-Nicetown section of the city.
Investigators say the victim, Larry Bennet, 67, was talking to two neighbors when the gunman came up, shot him twice in the abdomen, and fled.
The victim was pronounced dead around 1:20 p.m. at Temple University Hospital.
Detectives had to call for backup when they tried to apprehend their suspect, 17-year-old Tyrone Roberson, along the 1900 block of Rowan.
Tempers flared in the neighborhood between people who were suppportive of Roberson, and those who supported Bennett, who was known as "Mr. Larry," a handyman in the neighborhood who also sold fruits and vegetables from a cart.
"To do this in broad daylight, to shoot a 68-year-old unarmed man, we have to get him off the streets as quickly as possible," Capt. James Clark of the Philadelphia Police told Action News.
Friends of the suspect were reportedly making it more difficult for officers to track Roberson down.
By one account, an argument between Roberson and Bennett started, because the teen accused Bennett of stealing something from his mother's yard.
Police had to be called to the block several times Monday night to calm tensions on the block where both the suspect and the victim lived.
Roberson is described as a black male, 17 years old, about 5'6" to 5'7" tall. He was seen wearing a silver striped shirt and gray sweatpants. Anyone with information about his location is being asked to call 911.
