The 15-year-old victim was cycling along High Street, Dunsville, on Boxing Day when the incident occurred.
Police officers are trying to trace the man responsible.
He was white, around 50-years-old, tall, slim and had a grey, trimmed beard.
He was wearing a light coloured helmet.
A South Yorkshire Police spokesman said: "On Boxing Day a 15-year-old lad was cycling home on the pavement at the side of the A18, High Street, Dunsville.
"A male was also cycling behind him. For unknown reasons the male has passed the lad on his nearside and pushed him off his bike. He’s then carried on along his way out of sight.
"This may be a usual commute for this male."
Anyone with information on the incident or culprit should call South Yorkshire Police on 101.