The incident happened during a Hampshire Premier League game in Silchester on Saturday, December 11.
A Whitehill & Bordon FC player was assaulted after a penalty was awarded to Silchester FC in the 61st minute.
The man suffered a fractured cheekbone, a cut to his eye and a damaged tooth.
Although the incident occurred on December 11, it was only reported to police on December 31.
In a statement, Hampshire Constabulary said: ‘Officers have contacted both teams and Hampshire FA, but we are keen to hear from any other witnesses.
‘Were you in the crowd? Did you witness the incident? Do you have any footage or images that could help our investigation?’
Anyone with any information is asked to call 101 quoting 44210521014.
Alternatively people can call Crimestoppers anonymously on 0800 555 111 or online at https://crimestoppers-uk.org/