The victim was going in the direction of Sandsfield Lane bridge on his way to a local post office when he was attacked in broad daylight.
Mark Watson, prosecuting, said the victim was approached and asked if he had a spare cigarette. When the man said he did not have a cigarette he was accused of lying.
Mr Watson said: “He was then asked if he had any weed. He said ‘no’ and was then asked to get his wallet out.”
Henry Smith then joined in the incident running up to the victim and again demanded his wallet.
Mr Watson said: “The victim was punched to the face by Smith causing him to fall to the ground.
“The victim dropped the carrier bag he was holding and his attackers started grabbing him and pulling his jacket over his head.”
The attackers ripped both his jacket and his tee-shirt from the man and stole three mobile phones he was planning to despatch from the post office.
Police were called to the scene and although Smith ran off he was detained nearby.
A 15-year-old boy involved in the incident was arrested later.
Smith, 21, of Summergangs Lane, Gainsborough, and a 15-year-old boy each admitted robbery as a result of the incident on May 21, 2015. Smith was jailed for three years. The 15-year-old boy was given a 12 month supervision requirement with an activity requirement including 20 days of reparation. He was also ordered to have no contact with Smith for nine months.
Sunil Khanna, for Smith, said his client had moved to Gainsborough from Norfolk with the intention of making a fresh start living with his sister.
He said: “This wasn’t planned. He came across what he thought was a confrontation.
Michael Cranmer-Brown, for the 15-year-old, said his client has since moved away from Gainsborough.
He said: “His move has brought about significant changes in his life.
“He has been found accommodation. Other agencies have been involved and this young man has been responding well. He does seem to be maturing.”