Northern Rail tweeted at about 5.30pm on Wednesday, April 4 to confirmed that police were needed on a train between Halifax and Bradford Interchange.
This caused many trains to be delayed or cancelled by blocked lines.
Many commuters use this line to travel to and from Leeds stations Bramley and New Pudsey - as well as further afield towards Bradford, Calderdale and Manchester Victoria.
The company issued this statement on Twitter: "Due to passengers causing a disturbance on a train between #Halifax and #BradfordInterchange some lines are blocked.
"Train services running through these stations will be cancelled or delayed.
"Disruption is expected until 8pm. There is no estimate for the line to reopen at this time."
In a reply to a customer query, the company confirmed police were required to deal with an incident on the train.
British Transport Police confirmed today (Thursday) that the incident involved four people.
A British Transport Police spokesperson said: "Officers were called at 4.50pm last night following reports of aggressive behaviour on a train approaching Halifax.
"Officers attended the station and spoke to four people believed to be involved.
"Their details were taken while enquiries continue."
British Transport Police have asked anyone who witnessed what happened to contact them by texting 61016 or calling 0800 40 50 40 quoting reference 409 of 04/04/19.