A man was seriously injured when he was attacked by a stray Staffordshire bull terrier in Liverpool, police said.
David Morgan, 75, had to undergo surgery after the dog savaged his arm in the attack in Ferndale Road, Wavertee on Monday night.
The animal had earlier attacked a Shih Tzu dog and its owner, police said.
It is understood the dog then attacked Mr Morgan, who was standing between the animal and a boy of eight.
He was bitten when he got the dog in a headlock as he tried to bring it under control.
Officers were able to seize the Staffordshire bull terrier, which was without an owner and not on a lead at the time.
The Shih Tzu, its owner, and two other people were treated for minor injuries.
Insp Matt Boyle, from Merseyside Police's dog unit, said: "This was a particularly nasty incident involving what appears to have been a stray dog.
"Incidents involving stray dogs are very rare in Merseyside and every effort is being made to try to establish if the dog has an owner."