A 14-year-old girl was pushed by a man in Wollaston.
The incident happened in Newton Road, between 9pm and 9.15pm on Thursday, April 19.
The offender was a white man, tanned, about 5ft 5in, in his early 20s and wore a dark blue polo top and beige trousers.
Officers would like to speak to anyone who may have witnessed the assault or who has any information regarding it.
Witnesses or anyone with information can call police on 101 or Crimestoppers anonymously on 0800 555111.