A man was taken to hospital after being assaulted outside a pub in Holmfirth.
The attack happened between 1am and 2am, outside the Shoulder of Mutton pub in Dunford Road on April 23.
The victim, 30, was stood alone when he was approached from behind and punched twice.
He fell into a wall before hitting the ground and was treated in hospital for serious injuries.
A West Yorkshire Police spokesman said: "Officers are appealing for anyone who may have been in or around the pub during the evening, or who may have seen the incident itself, or who has any information to come forward.
"Information can be passed to DC Riley at Kirklees CID by calling 101 and quoting 13170183427. Information can also be passed anonymously to Crimestoppers on 0800 555 111."