A man and woman couple were said to be arguing, before a man aged in his early 20s from Harrogate was assaulted by the man.
The incident, which happened on Union Street, next to Jubilee Car Park, took place between 1.30am and 1.50am on Sunday January 14.
The victim required treatment at York District Hospital for an injury to his ear and was discharged following treatment.
North Yorkshire Police have released an appeal for witnesses and information to help establish the full circumstances surrounding the incident.
In particular, they are appealing for information from a taxi driver who may have driven a white taxi past the incident on Union Street around the same time and may have caught the incident on a dashcam.
Anyone with information that could assist the investigation should contact North Yorkshire Police on 101, select option 2, and ask for Beth Crawford-Evans.
You can also email [email protected]
If you wish to remain anonymous, you can pass information to Crimestoppers on 0800 555 111.
Please quote the North Yorkshire Police reference number 12180008069.