A woman grabbed another person by the hair and dragged her to the floor at a Leeds nightclub, police have said.
Police have released CCTV images as part of an appeal to trace a woman they want to speak with about the assault at Mission on Sunday, January 28.
The assault between 3.10am –and 3.20am, which was described by officers as "unprovoked", left a 19-year-old woman with a concussion which required hospital treatment.
In their appeal, they said: "A woman grabbed a 19-year-old woman by the hair and dragged her onto the floor.
"The attack is believed to have been unprovoked.
"The victim sustained concussion and required hospital treatment after the assault which happened at around 3.10am – 3.20am on Sunday 28 January.
Officers would like to speak to the woman shown in the CCTV images as she may have information which could help with the investigation.
Anyone with information is asked to call call British Transport Police on 0800 40 50 40 or text 61016, quoting reference number 123 of January 28.