Police are appealing for witnesses after a man was assaulted in Montagu Street, Kettering, on Friday (May 11).
The victim was walking down the road at about 11pm, heading towards Stamford Road, when he was approached from behind and punched in the back of the head.
A police spokesman said he was hit another three times and suffered bruising to his eye and arm.
It is believed there were two or three male offenders.
Witnesses, or anyone with information about the attack, is asked to call Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.