The incident happened between 5.30pm and 6pm on Saturday March 7 at the level crossing in Stein Road, Southbourne near Chichester.
The victim, a 69-year-old man, had walked from The Travellers Joy public house along Main Road and north up Stein Road towards the station when he was approached from behind.
The assault on him was unprovoked and left him shaken, but he did not require hospital treatment.
The suspect also shouted abuse at a family with a young child and two dogs. Officers are keen to speak with the family.
The suspect is described as being white, about 5’9” with light facial hair, wearing a baseball cap and carrying a dark rucksack. He left the area via an alleyway running behind the north platform at Southbourne station.
Witnesses or anyone with information, including anyone with CCTV, mobile phone, or dashcam footage from the area at the time, is asked to report it to Sussex Police online by quoting serial 751 of 08/03.