A disturbance occurred on the Largs-Glasgow train involving men and women, and police are appealing for information.
A British Transport spokesman said: "We were called at 7pm to a train travelling towards Paisley Gilmour Street station from Largs, to reports that there was a disturbance involving a number of men and women.
"Officers boarded the train at Paisley Gilmour Street and spoke to rail staff.
"We are now in the process of establishing the exact circumstances of the incident and will be looking at CCTV from the train."
Anyone with information is asked to contact BTP by calling 0800 40 50 40 or texting 61016 with reference 508 of 4 August.