It happened on Union Street, next to Jubilee Car Park, between 1.30am and 1.50am on Sunday 14 January 2018.
It involved a small group of people containing a man and woman couple that were said to be arguing, before a man aged in his early 20s from Harrogate was assaulted by the man.
The victim required treatment at York District Hospital for an injury to his ear and was discharged following treatment.
Police are requesting the public’s assistance to help establish the full circumstances surrounding the incident.
Police 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 Bethany.email@example.com
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.