North Yorkshire Police is appealing for witnesses to the incident, which took place in Coney Street at around 12.40am today.
The woman suffered a minor head injury as a result of the assault and was taken to hospital for treatment.
A spokesman said: "An 18-year-old man has been arrested in connection with the incident and remains in police custody at this time.
"Anyone who witnessed the assault or the events surrounding it is urged to contact North Yorkshire Police."
Email [email protected] or call 101, select option 2 and ask for PC 783 Hardwick.
Alternatively, call independent charity Crimestoppers on 0800 555 111 to pass on information anonymously.
Please quote reference 12190009753 when providing information.