It happened around 5:15 p.m. Monday on the 600 block of Long Lane.
Action News has learned that one man was pronounced dead at the scene. He has not been identified.
Police say another victim was shot and rushed to an area hospital and listed in critical condition. Two other victims were grazed by bullets and suffered non-life-threatening injuries.
Upper Darby Police Superintendent Timothy Bernhardt said the incident was retaliation for a fatal shooting that happened last week in Clifton Heights.
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In that incident, police say Birchett King, 25, shot and killed his uncle, 39-year-old James Ford, after a fight over a car.
A funeral was held for Ford on Monday, along with a luncheon that followed on Long Lane in Upper Darby.
Between 50 to 100 people were gathering at the venue when the shots rang out.
According to Bernhardt, at least one gunman exited a dark-colored Chevy Malibu and opened fire.
"Everyone that was on location here were coming out of that venue. Of course, they were running they were scared," said Bernhardt.
No arrests have been made in connection with Monday's shooting.
Meanwhile, police in Clifton Heights say Birchett King was taken in to custody on Monday. It's still unclear if he had any involvement with the shooting on Long Lane.
Anyone with information on this case is asked to call the Upper Darby police.