A police officer was attacked outside a Rotherham nightclub when he tried to split up a group of men fighting.
The 51-year-old suffered head injuries after he was repeatedly punched after intervening in a brawl between a group of men outside The Loft in Ship Hill.
Police said the culprit ran off.
Detectives investigating the incident have released a CCTV image of a man they want to trace.
A South Yorkshire Police spokesman said: “At around 2.20am on Saturday, August 22, police were called to reports of disorder in Ship Hill, near to The Loft nightclub.
“A number of men are believed to have been fighting and, when officers tried to intervene, it is alleged that one man punched an officer several times before fleeing the scene.
“The 51-year-old officer sustained head injuries.
“Extensive enquiries have been undertaken since the assault and three men have received cautions for public order offences in connection with the incident.
“Police believe the man pictured could hold vital information and would urge anyone that can help with enquiries to come forward.”
Call 101 quoting crime reference number C/87281/2015 or Crimestoppers on 0800 555 111.