Train damaged before Sunderland Middlesbrough FA Cup tie
Rail staff were assaulted and a train badly damaged by football fans on their way to the Tees Wear derby on Wednesday night.
British Transport Police (BTP) said a window and lights were ripped out and seats badly damaged on the 17.50 Sunderland to Middlesbrough service.
They are also investigating reports two members of rail staff were assaulted.
A BTP spokesperson said: "We will not tolerate incidents such as this by so-called football fans."
She added: "Passengers and rail staff have the right to travel and work without being subjected to the type of behaviour shown during this incident."
The incident happened before the match between Middlesbrough and Sunderland after a large number of fans boarded the Northern Rail service at Sunderland.
BTP said the disorder, which involved a "small group" of these fans, meant the train had to be terminated at Hartlepool and the fans put off on to the platform.
Police are studying CCTV footage.