Eight police officers have been injured after being confronted by a crowd in Dalston, east London, on Friday evening.
Police responded to a request for support by a ticket inspector after a teenager was found not to have a valid ticket.
The situation quickly become violent and the responding officers required back up.
The officers sustained facial injuries including cuts and bruises and two were taken to hospital with concussion.
Two teenage girls and an 18-year-old man were arrested over the incident on Kingsland High Street.
A 15-year-old girl was arrested on suspicion of fare evasion and assault on a police officer.
The man and a 16-year-old girl were held on suspicion of assaulting a police officer.
All of the police officers have now been discharged from hospital.