Naomi Spencer, 45, who has a 15-year-old son, was on her way home from work when six well-built youths burst into her carriage in pursuit of a blood-soaked man.
The youths were verbally and physically abusive to him until brave Naomi stepped in.
Telling them to 'pack it in' she broke the victim away from his attackers and, as though they were naughty children, ordered them to go and sit at opposite ends of the carriage.
When the belligerent youths threatened her, Naomi said she simply silenced them with 'the look' she gives her own teenager when he is playing up.
"They were like children in a playground, it was embarrassing. I just wanted them to stop," said Naomi.
"They shouted at me about why they were arguing but I said I didn't care. I told them it was six on one and it was out of order. They were quite shocked - I was just giving them clear instructions and they stood back and just did it."
The Sun reports that fearless Naomi was treated to a round of applause from the other passengers after her intervention.
The British Transport Police have now given her a certificate of commendation to thank her for her actions.
Chief Constable Andrew Trotter said Naomi had stopped the situation from escalating, and that she was very brave.
"I was very pleased to be able to present Naomi with such a prestigious award for her incredibly brave actions, which were absolutely outstanding and undoubtedly prevented the situation between these two groups becoming far worse," he said.
Naomi, from Crediton, Devon, said she was surprised to have got the award.
"I was pretty shocked that I got the certificate but I was proud as well, it is a great thing to have and I didn't do any of this to be recognised for it," she insisted.