A train was halted by police when bagels were flung around a carriage by rowdy passengers who then started fighting.
The baked goods-based disturbance resulted in the train being stopped at Potters Bar, Hertfordshire, just after 01:00 GMT on Sunday.
Video posted on Twitter showed women placing bagels on a man's head before he threw them out of the window.
The train was held for 18 minutes while police took statements.
During the video, a group can be heard singing: "He's got a bagel on his head" to the tune of "He's Got the Whole World in His Hands".
The footage also shows brawls in the carriage and outside on the platform. It is not known if these were connected to the bagels.
Two officers later board the train and ask passengers for an explanation.
British Transport Police (BTP) tweeted about so-called "BagelGate", telling passengers: "Let's be clear, no bagel should be treated so cruelly. And no one subjected to intimidating behaviour."
The video of the incident has been liked 17,000 times and had more than 10,000 retweets.
A spokeswoman for Great Northern, the operator of the 00:54 service from King's Cross to Huntingdon, said: "We take all incidents of intimidating behaviour on our services very seriously and encourage passengers to report them to the BTP."
No arrests have been made.