The 17-year-old victim, who has not yet been named, was fatally injured in Back Seaforth Avenue, Harehills, at around 12.40pm.
He was taken to Leeds General Infirmary but his death was confirmed a short time later.
One man, who looks after his father in a house that overlooks the spot where the incident happened, said it was obvious the victim would not survive.
He said: “You could tell he was dead. I don’t know why they were even trying to save him.
“There are loads of problems round here. There’s people from one street who regularly fight with a group from another street.
“You’ll probably get three or four bad incidents a year, just not this serious.”
Police cordoned off a large area as they carried out investigations.
Two forensic tents were erected at the spot where the attack happened.
Officers from West Yorkshire Police’s Homicide and Major Enquiry Team were continuing to look for the culprits.
Harehills and Gipton councillor Roger Harrington said problems with anti-social behaviour in the area were well documented.
“There hasn’t been anything this serious but there have certainly been issues,” he said.
Police are appealing for information. Call Stainbeck CID via 101.