A 19-year-old woman was pushed to the floor and punched several times in Northampton town centre.
The attacker, described as an Asian woman in her late teens, was stopped by members of the public who intervened after the assault near Tesco Express
in Wellingborough Road.
Officers are keen to speak to the people who helped the victim. The assault happened between 5pm and 5.30pm, on Thursday, August 22.
The attacker 5ft 2in, with a very slim build. She had long dark hair, tied up in a ponytail.
Witnesses to this incident, or anyone with any information, can call Northamptonshire Police on 101.
Alternatively, information can be given anonymously to Crimestoppers on 0800 555 111.