The assault took place at the Splendour Festival at Wollaton Park on Saturday, July 18.
It happened in front of the main stage around 9.20pm during a set from The Specials.
The victim of the assault sustained injuries which needed hospital treatment.
Nottinghamshire Police are keen to speak to the man in the above picture.
Anyone who may know this man, or have any information which could help the investigation, call 01 quoting incident number 958 of 18 July.
Alternatively, call Crimestoppers anonymously on 0800 555 111.