A male in his 20s was allegedly punched in the face and left with a black eye after trying to intervene in an argument between a man and a woman last weekend.
The incident happened at around 1.45am on Sunday, May 27 in St Martins Square in Lincoln.
An image of a man has been released who police believe can assist with enquiries into the reported assault.
Anyone with information, or who recognises the man, should contact police on 101 quoting incident number 47 of May 27 or via email at [email protected]
It can also be reported through the independent charity Crimestoppers anonymously on 0800 555 111 or online here.