The incident happened on Beastfair at around 2.30am.
The victim was taken to hospital with non-life threatening injuries.
A 27-year-old man has been arrested in connection with the assault and has been bailed pending further enquiries.
Detective Inspector Tim Hunt of Wakefield CID, said: “We have launched an investigation into what happened and I would appeal for any witnesses who have not yet come forward to contact police on 101 quoting log 109 of Wednesday 29 March.”
Information can also be passed anonymously to independent charity Crimestoppers on 0800 111 555.