An 18-year-old man was assaulted in Castle Fields Park, Wellingborough, on Monday afternoon.
The teenager was approached by a woman at about 2.40pm, who asked for a cigarette. He offered her one and she grabbed the pack from him and walked away.
At this point a group of three men then approached the victim and pulled him to the ground, punching him to the face causing a small cut.
His bag was searched but nothing else was taken, although his glasses were damaged in the incident.
The incident happened in the area of the park nearest to Castle Street and Irthlingborough Road.
One of the offenders was white, aged in his late teens, of thin build and about 6ft. He was wearing black tracksuit bottoms and a light blue tracksuit coat, black Snapback cap and was carrying a bag.
The woman who asked for a cigarette was also in her late teens, white, with blonde, shoulder length hair, of thin build and about 5ft 2ins. She was wearing a white top and black jeans.
Police would like to speak to anyone who may have witnessed this incident or who may have any information regarding it.
Witnesses or anyone with information is asked to call police on 101 or Crimestoppers anonymously on 0800 555 111.