A “boy” who allegedly forced his way through a tube station's ticket barriers, assaulted a London Underground worker who confronted him about not paying the fare, police said.
After an initial struggle, the Transport for London (TfL) employee was pinned against the wall, slapped in the face and kicked in the stomach.
The incident at Bounds Green station on the morning of 27 June was captured on CCTV.
Three people quickly intervened, dragging the suspect away to prevent him from landing further blows. One appeared to be a fellow TfL employee.
Investigators from British Transport Police (BTP) said they were hoping to trace a boy wearing a grey tracksuit who intervened.
He had been travelling with the suspect and the two left the station together, a spokesperson for the force said.
Images of the pair were released in August, but neither has been identified.
Officers believe the two were younger than 18 years old.
TfL’s managing director of London Underground, Vernon Everitt, said staff were working closely with the police “to identify the perpetrator and bring them to justice”.
He added: “This was an appalling and dangerous attack on a member of our staff,” Mr Everitt said. “Everyone has the right to go about their day without fear or intimidation and we do not tolerate any form of physical or verbal assault on our staff or customers.”
The attack came days after a 23-year-old man was handed a 12-month suspended sentence after he knocked down a TfL staff member who confronted him about forcing his way through the ticket barrier at London Victoria station.
That Tube worker suffered serious injuries to his arm.
Anyone with information about the boys in the CCTV footage is encouraged to contact BTP.