In the run-up to the attack on December 11 last year, members of the public witnessed defendant, Alan Jones, becoming involved in a physical fight with another man that subsequently led to him being headbutted, Sheffield Crown Court heard.
"The elderly man was concerned for his wife, and some children who were in the area, so asked Jones to move the disagreement away," said Olivia Murray, prosecuting.
She added: "He ran at the man at hit him on the right side of the man's jaw with his clenched fist. The man dropped the bags of shopping he was holding."
Members of the public came to the elderly man's aid by apprehending Jones and calling the police, before taking the elderly man into a nearby branch of Thomas Cook in Doncaster town centre to check him over.
Through his victim personal statement, the court was told how the attack had left the elderly man feeling 'embarrassed,' but said he had been heartened by the help he received from members of the public had which had left him with 'tears in his eyes'.
In mitigation, William Louw said: "My client was under the influence of spice and was very intoxicated while this was taking place."
Jones' next lot of offending took place at around 4am on February 27 this year, when police approached him on Sunny Bar in Doncaster town centre and found him to be in possession of a black gurkha-style knife.
When asked about the knife, Jones, aged 41, told officers that he had found it, and led them to a rucksack in which they discovered a number of items that had recently been stolen from an army surplus market stall.
Jones then carried out two lots of criminal damage in Doncaster town centre.
On March 3 he smashed the glass door to Specsavers Opticians in St Sepulchre Gate causing £440 of damage, before causing £50 of damage a police bike chained up outside Subway on March 11.
Jones, of no fixed abode, pleaded guilty to charges of assault, possession of a bladed article, theft and criminal damage on the day he was due to stand trial for each of the offences.
Mr Louw added: "This is a 40-year-old man who has spent a considerable amount of time with drug and substance misuse issues."
Judge Sarah Wright sentenced Jones to 19 months in prison.
She said: "You are a persistent offender who causes a great deal of upset and loss to very many people by your unlawful actions."
*South Yorkshire Police have been asked to provide a custody image of Jones