YOBS rifled through the pockets of an unconscious man who was punched in an unprovoked attack.
William Salcombe, 22, knocked out mortgage advisor Paul Bantock, leaving him bleeding from his head and with a broken ankle.
He was jailed for 30 months after admitting inflicting grievous bodily harm at Gloucester Crown Court.
Mr Bantock was set upon as he walked past Salcombe and 12 to 15 of his friends near Morrisons in Abbeydale last August.
Salcombe, of Perry Orchard, Upton St Leonards, said "brace yourself" before punching Mr Bantock, 28.
Mr Bantock's girlfriend, Maureen Hodges, was also hit in the face by another of the youths, who began going through Mr Bantock's pockets while he was passed out.
Prosecutor Julian Kesner said Mr Bantock's parents came to the scene and described it as the "worse nightmare imaginable".
Salcombe told police he had been defending his younger disabled brother, who said Mr Bantock had threatened him.
But Mr Kesner said: "The crown does not accept there was any provocation or excuse to act the way he did."
In a victim impact statement the couple said they were still living with the consequences.
Mr Bantock needed an operation, 10 weeks off work and was on anti-depressants.
Steve Young, in mitigation, said: "His explanation, which he gave to the police, is that he was contacted by his younger and disabled brother, who he feels protective of, who said he was being threatened and so he punched him."
Recorder Peter Towler told Salcombe: "I accept your brother is vulnerable, but I do not accept it was in anyway necessary for you to punch him."
After the case, Mr Bantock said he was pleased with the sentence.
He said: "It is difficult to go back to the place it happened and I can no longer do my shopping there. It has been horrendous."