A group believed to be Scunthorpe United fans subjected passengers to lewd comments and a sexual assault, on a train from Rotherham to Doncaster, police have said.
British Transport Police are seeking information on the incident, which happened between 5.53pm and 6.45pm on Saturday, October 14.
Rotherham United had just defeated Scunthorpe United 2-0 at the AESSEAL New York Stadium.
The men, who were thought to be Scunthorpe United fans travelling back from the game, are said to have made unwelcome remarks to fellow passengers before a woman was assaulted at Swinton.
The 23-year-old stood up to leave and was sexually assaulted by one of the men involved, according to the British Transport Police.
They would like to speak to anyone on the train who witnessed the incident, or anyone with information which could help the investigation.
They urge such people to call British Transport Police on 0800 405040 or text on 61016, quoting reference number 200 of November 9.