A woman was assaulted in Bridge Street, Northampton, early on Sunday, January 18.
The woman was walking along Bridge Street with a group of friends shortly after 4am when an argument broke out with a group of two or three men.
She was punched in the face and her jaw was broken.
A man has been arrested and bailed pending inquiries.
Witnesses should call Northamptonshire Police on 101 or Crimestoppers on 0800 555 111.