A 57-year-old man was sprayed in the face with an aerosol after a dispute on the Queensway estate in Wellingborough.
Police are appealing for witnesses to the incident which took place on the grass area at the bottom of Minerva Way at about 6.30pm on Saturday, March 22.
The offender was a white man, believed to be of Eastern European origin, between 5ft 10in and 6ft, of medium build, 25 to 30-years-old, with short dark hair and clean shaven.
He wore a black tracksuit, white trainers and was on a bicycle.
Anyone with information about the incident can call the police on 101 or Crimestoppers anonymously on 0800 555111.