A group of youths left a passer-by with facial injuries after assaulting him in a park.
The 63-year-old victim had been in Hirst Park, in Ashington, when the assault happened between 7.50pm and 8.02pm on Sunday, May 28.
The man had intervened as a large group of youths had been drinking in the pavilion area of the park and behaving in a rowdy manner.
Youths then attacked the man, punched him to the face causing him to fall to the ground and those responsible ran off.
An ambulance was called and the man was taken to Northumbria Special Emergency Care Hospital in Cramlington, where he was later discharged following treatment.
Police are appealing for witnesses to the incident to come forward.
Inspector Liz Hall said: “We carrying out additional patrols in Hirst Park to prevent further anti-social behaviour incidents and to reassure the public.
“This attack is completely unacceptable and such behaviour will not be tolerated in our community.
“We are determined to ensure we keep the park as a safe and pleasant environment for residents and visitors of all ages to enjoy.
“We know it’s only a relatively small number of young people who are responsible for this attack and the vast majority are well behaved.
“So it’s important we tackle this problem effectively to prevent any recurrence.
“We would urge anyone who saw the incident to speak to police.”
Following enquiries two teenage girls, aged 13 and 14, have been assisting police with their enquiries.
Anyone with information should call police on 101, quoting reference number 1056 of 28/05/17 or ring the independent charity Crimestoppers on 0800 555 111.