Surveillance video shows the moment a man enters Colletti's Town Tavern on Marshall Street on Wednesday evening.
"We kindly asked that he take the dog outside, and the guy wouldn't listen to us," said Alex Ngove, Colletti's business manager.
He said, a moment later, the suspect grabbed his uncle Thong's arm and pulled him toward the dog. The dog bit Thong's hip and leg several times.
"I hear my husband yelling and screaming with the pain," said Heng Ly, the victim's wife.
Thong Ngove, the bar's owner, was on the ground in pain until medics arrived.
He was taken to Suburban Hospital with multiple bite marks on his hip and leg.
The suspect, who witnesses say lives nearby, got away with his dog.
"He's been here before, he's a regular customer of ours, and we've told him multiple times," said Alex Ngove.
Norristown police are investigating.
The Ngoves have owned Colletti's for 20 years, and are still open while Thong recovers at home.
Police say witnesses have identified the suspect. An arrest has not been made.