He was a passenger on a Northern service when he was struck on his head at 11.40pm on Tuesday, September 24.
The victim was left with bruising and a cut, which required hospital treatment.
A 25-year-old Doncaster man was arrested on suspicion of causing grievous bodily harm.
He has been bailed pending further enquiries.
Anyone with information should call British Transport Police by sending a text to 61016 or by calling 0800 40 50 40, quoting reference 1900082664.