A former soldier and off-duty policeman needed hospital treatment after a "thuggish" confrontation when he asked a gang using a lighter in the street to move the flame away from his face.
The ex Royal Marine, now a serving police officer who was off duty, suffered cuts to his head, with bumps and bruising to his face after the street attack in Sunderland city centre.
Newcastle Crown court heard blood was "streaming" out of a wound to the victim's head after the violence.
A judge said the victim "deserved respect" not an "unprovoked beating".
The heard the victim had been walking through the town centre in April when he encountered four younger men on Vine Place and one was using a lighter with a "big flame".
After the victim pushed the lighter away, some of the group started "shouting and swearing", surrounded him, and he was pushed to the ground, where he hit his head on a shop window ledge.
In a victim statement, the former squaddie said: "The men looked hyped-up. It didn't take much for them to turn on me.
"I had been surrounded by them."
Danny Matuszek, of Gleneagles Road, Sunderland, admitted he "back handed" the victim, which led to his fall to the ground, and pleaded guilty to unlawful wounding.
The 20-year-old, who was on a suspended prison sentence at the time, has been jailed for 25 months.
Leon Parkin, of Lanton Street, Sunderland, admitted affray and having an offensive weapon in relation to a knife he was carrying, but did not produce, during the confrontation and discarded shortly afterwards.
The 19-year-old, who was out on licence from a previous prison sentence, has been jailed for 16 months.
A third defendant had his case transferred to the youth court.
Mr recorder Simon Goldberg told the court: "One member of the group held a lighter to the complainant's face.
"He pushed the lighter out of the way and asked you to stop what you were doing.
"Another of the group took exception to his entirely reasonable request and began shouting and swearing at him.
"He was then surrounded by the group and struck by Mr Matuszek with such force to cause him to fall to the ground, at which point, he felt blood running down his head."
The judge told the men: "This was a completely unprovoked and thuggish attack on an innocent man simply minding his own business.
"He is a former soldier and serving policeman.
"He deserved your respect and what he got was an unprovoked beating.
"This was in full view of the public, in the middle of the day."
Jamie Adams, defending, Matuszek, said the group had not been causing any trouble before the victim approached them, had not intended to commit any offence that day and that they immediately backed away after the confrontation.
Mr Adams said Matuszek has a good work record and a chance of employment after his release.
He added: "He is young enough to progress and make progress, that is something he has done druing teh time he has been in custody.
"He wants to work, wants to be constructive in his life."
Tony Cornberg, defending Parkin, said the teen feels he has "let everyone down" but has made good progress and completed educational courses in custody
Mr Cornberg added: "He can't spend his life in and out of prison."
Detective Sergeant Gaye Martin, of Northumbria Police, said: “This was an unacceptable and random attack on an off-duty officer who was going about his every-day life.
“Assaults such as these are rare in the city centre, but we take any reports we do receive extremely seriously. These individuals left their mark on the victim, who was hospitalised as a result of their callous actions.
“They must now deal with the consequences of their crimes.
“I would like to take this opportunity to praise the victim for their cooperation throughout this case, as well as the tireless hard work and dedication of my team to ensure those responsible had their day in court.”