A woman was assaulted as she walked through a small wooded area close to a supermarket in Kettering.
The woman was walking in the Malham Drive area, close to the Asda supermarket, when she was attacked.
The incident happened sometime between 4.40pm and 5.30pm on Friday, December 11.
The man, who was white, grabbed the woman from behind before hitting her on the head.
Witnesses, or anyone who knows anything about the incident, can call Northamptonshire Police on 101 or Crimestoppers anonymously on 0800 555111.