A 39-year-old man suffered a broken arm and face injuries when he was attacked in Haley Hill in Boothtown, Halifax, at 10.30pm on Saturday.
Officers want to find two men described as white, in their early 20s.
One had a shaved head, was just over 5ft 7ins tall and wearing a black or brown shirt.
The other was about 5ft 8ins tall, with slim facial features and wearing a black hooded top. Anyone who can help should call 01422 337086.