Sheffield Wednesday and Chesterfield fans are among those believed to have been involved in a mass brawl on a train.
Owls fans on their way back to Sheffield after an away game at Brighton are thought to have been among those who ended up fighting with Chesterfield fans at Leicester train station on Saturday, August 9.
Two groups clashed, leaving a number of people with injuries, on the 8.56pm London to Sheffield service as it pulled in at Leicester at around 10pm.
CCTV footage is being examined and witness statements have been taken.
PC Marcus Gale, who is leading the investigation, said: “Around 20 people, men and women, became involved in an altercation as the train pulled into Leicester station.
“A number of people received minor injuries as a result, and the service was delayed for more than 21 minutes.
“We believe the people involved may have been travelling back from the Brighton v Sheffield Wednesday game, along with another group travelling back from the Leyton Orient v Chesterfield match.
“We would like to hear from anyone who was travelling on the service, or who was at the station and may have witnessed the incident.
“We take all allegations of anti-social behaviour, racial intolerance and football-related disorder on the rail network very seriously.
“Staff and passengers, as well as law-abiding fans, should feel entitled to travel on trains without having to worry about the actions of a small minority of people who fail to conduct themselves properly.”
As the new Football League and Premiership seasons get underway, British Transport Police and train companies have pledged to step up efforts to ensure fans and other passengers have trouble free journeys on match days.
Police are urging rail staff and members of the public to report all incidents of anti-social behaviour.
Passengers can ‘discreetly’ report crime and disorderly behaviour using BTP’s 61016 text number
A British Transport Police spokesman said: “British Transport Police is making renewed efforts working with the rail industry to identify the small number of violent, drunken, disorderly or racist individuals who give clubs and football generally a bad name.
“Fans who get very drunk, will find they are not allowed to travel; if they are disorderly, they will be removed from trains; if they are violent or racist they will be arrested and banning orders will be sought against them.
“BTP will use CCTV, uniform and plain clothes officers to identify those responsible and then take action against them.”
Anyone with information should contact British Transport Police on 0800 405040 or by text on 61016.