Five men attacked a 46-year-old after he challenged them for making sectarian chants on a train.
The victim sustained a facial injury and cut to his head during the incident at around 9pm on Saturday.
British Transport Police said the attack took place as they travelled on the 8.18pm Glasgow Queen Street to Alloa service near Larbert, near Falkirk. It is understood the group travelling on the train had attended the Rangers versus Queen's Park game at Hampden earlier that day.
After the attack, the group disembarked the train at Stirling station. Derek Jackson, the investigating officer, is appealing for information.
He said: "The victim was subjected of a deplorable attack and I am anxious to trace those responsible as a matter of urgency. If you have any information please come forward."
One of the attackers is described as being of stocky build with short brown hair and was wearing a khaki body warmer.
A second suspect is described as being around 50 years old and was wearing dark clothing, while a third was around 5ft 10in and was wearing a quilted jacket.
Anyone with information relating to the attack is asked to call British Transport Police on 0800 40 50 40.