South Yorkshire Police are appealing for information about an incident outside The Wilton pub in Kimberworth Road, Rotherhham, on Sunday (October 30).
It is reported a 29-year-old man was waiting for a taxi outside the pub at about 4.30am when a man on a motorbike stopped and tried to take his mobile phone.
After refusing to give it to him, the man on the bike is said to have assaulted the victim, causing minor injuries to his face.
The rider then stole the phone and rode off toward the town centre on what is believed to be a trails style bike.
The rider is described as white, in his late teens, with short black hair. He is believed to be between 5ft 8ins and 5ft10ins tall, reportedly speaking with a local accent. He was wearing dark coloured clothes with white helmet with black stripe on.
If you have any information contact 101 or email firstname.lastname@example.org quoting incident number 384 of 30 October 2016 or anonymously to Crimestoppers on 0800 555111.