A 34-year-old woman was attacked at a bus stop in Eastern Road, Brighton, on Saturday (21 June).
The victim received a minor injury to her head after she was assaulted while waiting for a bus at 10.50pm.
There is believed to be one suspect who is described as a white man, about 25 to 30 years old, 5ft 7in tall and of muscular build, with a baby face and short mousey brown hair.
He was wearing a white t-shirt, blue jeans and trainers.
PC Jane Everson said: “This attack has left the victim very shaken.
“We are asking for anyone who witnessed this incident to come get in contact with us. In particular we would like to speak to a man who helped the victim and stopped the attack.”