Scotrail confirmed the incident on the 5.16pm Edinburgh-Glenrothes service which caused it to terminate at Kirkcaldy.
It also warned other services could be delayed or disrupted as result of the investigation.
The rail company tweeted an alert to passengers which warned: “Due to passengers causing a disturbance on board a train at Kirkcaldy, services through the area will be cancelled, delayed or revised.”
It added that transport police had responded and Scotrail staff were assisting them.
Scotrail then tweeted: “The 1716 Edinburgh–Glenrothes has had to terminate at Kirkcaldy due to passengers causing a disturbance on board the train. We’re sorry if you’re affected by this.”
No further details on the incident were given.
The trouble came as commuters in Fife started to back a new petition calling for major improvements to the Fife Circle service.
Launched by James Bell, it calls on Michael Matheson, Cabinet Secretary for transport, infrastructure and connectivity, to tackle the long-standing problems which have left many Fife commuters frustrated in 2018.
It said: “Commuters on the Fife Circle Line are being badly let down by late running trains and cancellations. Last minute platform changes, poor communication and overcrowding further add to the increasing frustration experienced by Fife Circle Line commuters.
“The problem has deteriorated to an unacceptable level causing disruption, distress and undermining confidence in the train system as a reliable means of transport.”
The petition has already attracted 220 signatures.