A teenager needed hospital treatment after being attacked by a man in York city centre.
Police are appealing for witnesses after the assault which took place at about 2.30am on Sunday (October 30).
The 17-year-old victim was on Clifford Street, outside Kuda, when he was assaulted. The offender was part of a group of men, some of whom were wearing fancy dress.
The victim, from Copmanthorpe, suffered a serious injury to his mouth, which required hospital treatment.
A 21-year-old man from Haxby was arrested on suspicion of assault in connection with this incident. He has been released on bail pending further enquiries.
Anyone who witnessed the incident, or who has any information about it, is asked to contact North Yorkshire Police.