A punter suffered a fractured skull after intervening in an argument at a Leeds pub.
Police have now released CCTV images of a man they want to trace over the incident in Horsforth.
The 46-year-old victim was punched to the ground as he was leaving the Kings Arms, in Town Street, in the early hours of Sunday.
Police believe the unprovoked attack was connected to an earlier incident when he intervened in an argument between two customers.
The attacker was white, about 5ft 7ins to 5ft 9ins tall, and aged in his late 30s.
He was described as slim, with a stocky chest and arms. He had short dark hair in a messy style and was clean shaven and was wearing a beige jumper and blue jeans and is believed to be a regular customer at the pub.
The victim has been receiving treatment in hospital but his injuries are not thought to be life-threatening.
Anyone with information should contact Detective Constable Lee Swift at Weetwood police station via 101 or call Crimestoppers anonymously on 0800 555111.