Detectives are appealing for witnesses after a teenage girl allegedly punched a member of staff in an attack at Denmark Hill station.
The incident happened at approximately 5.30pm on Saturday 15 April when a girl attempted to travel without a ticket, police say.
When challenged by a member of staff, the 17-year-old became verbally abusive, it is claimed.
Police say she then punched the male member of staff in the face who needed hospital treatment for a facial injury.
Officers are now appealing for any witnesses to come forward as soon as possible.
In connection with this assault, a 17-year-old girl from Lambeth was arrested on suspicion of common assault.
You can contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 209 of 19/04/2017. Alternatively, call Crimestoppers on 0800 555 111.