A police officer was punched, dragged to the ground and stamped on and her colleague was left unconscious as they dealt with a large fight outside a pub.
The officers were passing The Assheton Arms in Greater Manchester in the early hours, when they spotted the brawl.
The offenders fled the scene in Middleton after the female officer was stamped on and her male colleague was knocked out with a punch to the head.
Both officers were taken to hospital and have since been discharged.
Det Sgt Tim O'Callaghan said: "This is a disgusting way to treat police officers, who spend their days and nights trying to keep the people of Greater Manchester safe.
"We are providing welfare support to the two officers who were attacked after bravely trying to intervene in a large fight and keep the peace.
"We will not tolerate this kind of behaviour and are 100% committed to bringing those responsible to justice."
The attack happened after "Mad Friday" - the last Friday before Christmas, which sees a spike in alcohol-related incidents, and has become one of the busiest days for the emergency services.
The offenders are white and of medium build, Greater Manchester Police said.
One is described as having short brown hair and a beard, and wearing a dark shirt, trousers and trainers.
The other man is described as being about six feet tall and in his early 30s, with short dark hair and stubble.
He was wearing a black belted coat, jeans with ripped knees and dark shoes.