A swarm of high-powered bikes had almost taken over all three lanes of a New York street.
Caught between them was a 33-year-old Range Rover driver, his wife and their two-year-old daughter.
When one of the motorcycles apparently slowed to a near-stop in the centre lane, it was struck by the vehicle and its rider was knocked to the ground.
The SUV and its occupants stayed put at first. But moments later, surrounded by the fallen biker's fellow riders, it sped through the crowd and set off a chase, The New York Times reported.
The chase ended in violence after the SUV got stuck in traffic.
Several pursuing motorcyclists pulled the driver from the vehicle and beat him, police said.
The six-minute video of the incident, which happened on Sunday, has since gone viral.
New York police commissioner, Raymond W Kelly, said the motorcyclists had been part of a planned but unauthorised event in which hundreds of riders gathered outside of Manhattan and intended to descend en masse into Times Square.
The New York Post identified the SUV driver as Mr Alexian Lien and his wife as Ms Rosalyn Ng.
Police revealed the bikers started to damage the vehicle after Mr Lien hit a motorcyclist.
Fearing for the safety of his family, he sped off, hitting several other bikers on the way.
The family was eventually brought to a standstill in Manhattan traffic and immediately, bikers began to attack the vehicle.
One biker removed his helmet and threw it against the driver's window, smashing it; the second tries to punch through the rear door window, where the child was seated.
Then the footage stops. The video has already received many comments, most of them in support of Mr Lien.