An 18-year-old man needed hospital treatment for facial injuries after the incident on Westgate on Saturday, May 16.
Police said the Scunthorpe man was punched at the junction with Market Place following an argument between two groups of people in a bar.
It happened between 10.30pm and 10.50pm, police said.
They have released a picture of a man they want to speak to in connection with the alleged assault.
DC Laura Wheatley of Wakefield CID, said: “We are investigating this incident in which the victim sustained a serious facial injury which required surgery.
“There is a suggestion he may be from the Barnsley area and I would like to speak to anyone who recognises the man pictured who we would like to speak to in connection with what took place.
“Information can be given to Wakefield CID at West Yorkshire Police on 101 or the Crimestoppers charity, anonymously, on 0800 555 111.”