Lisa Robinson, 41, was on the train with her husband and son, five, when they were verbally abused by Cardiff City fans after a win over Millwall.
She stepped on to the tracks at Ystrad Mynach until police arrived.
The train was terminated and the fans had to end the journey on foot. British Transport Police are investigating.
Ms Robinson, a civil servant, and her husband Peter, 61, were on a day trip to Cardiff on 25 September to celebrate the their son's birthday and were returning home.
She said about 30 drunken Cardiff fans were on the Penarth-to-Bargoed Arriva Trains Wales service, celebrating their team's win after an early home kick-off against the London club.
She said things turned nasty when they began shouting sexist chants at a woman on the platform at Lisvane railway station and Ms Robinson asked them to stop.
She said: "Then their chanting became directly to me and it became sexist and quite obscene until by the time we got Caerphilly, I pulled the red handle and stopped the train."
The train driver came out and Mr Robinson asked him to call the police, but the driver reset the handle and continued with the journey.
The family were then "effectively trapped" on the train until they arrived at their home station of Ystrad Mynach, said Ms Robinson.
At the station the family got off the train and Ms Robinson again asked the driver to call the police but he refused, so she decided to take "direct action".
Ms Robinson said: "I slithered down off the platform on to the track.
"I wanted to protect both my husband and my child and I wanted this behaviour to stop.
"Some of the fans got off the train and took pictures of me with mobile phones and continued to abuse me.
"This is my community, this is my village. We're not going to be bullied and certainly for women and families, they should be able to travel on the train in peace and quiet and go about their business without being bullied like that."
The police were eventually called, and the service was terminated.
Wayne David, Labour MP for Caerphilly, called the "apparent inactivity" of Arriva Trains Wales and British Transport Police "unacceptable" and said he would be in touch with them about the incident.
"No member of the public should be subject to abuse of this kind and it must never happen again," he added.
British Transport Police said: "BTP officers attended Ystrad Mynach railway station after a report that a woman had been verbally abused by a group of football fans after she challenged their behaviour on board the train.
"BTP does not tolerate anti-social behaviour of any nature on the railway network and will do everything it can to identify offenders and bring them to justice."
Peter Northcott, head of stations at Arriva Trains Wales, said: "We take all complaints very seriously and I personally contacted Mr and Mrs Robinson on the day of this incident.
"A full investigation is taking place with the British Transport Police."
This woman is kind of my hero right now.