The man was injured as he bravely struggled with two men trying to steal a crate of beer from a Horsham off licence.
The men entered The Bottle Shop in Crawley Road just after 8pm on last Friday and when challenged punched the 33-year-old victim and hit him on the head. They then ran from the shop and down Littlehaven Road.
PC Martin Upton, of Sussex Police, said: “We would like to speak to anyone who witnessed this incident or who has any information about the suspects. The men, pictured in a CCTV image, are both described as white, in their mid-20s, skinny and with short hair.
Anyone able to help is asked to email email@example.com or call 101 quoting serial 1514 of 22/05. Alternatively, contact the independent charity Crimestoppers anonymously on 0800 555 111.”
Polcie said a third man, a 28-year-old man from Horsham, was arrested on suspicion of robbery and was later bailed until July 10.