Thomas Stubbs had to have a plate inserted in his jaw when it was fractured by a punch which floored him.
His assailant, Andriosky Hernandez- Sanchez, 23, was convicted of inflicting grievous bodily harm at the city crown court after the jury rejected his claim that he had been acting in self-defence during a flare-up between two groups.
Hernandez-Sanchez, of Maybush Road, Southampton, received a 12-month suspended sentence and an order to do 250 hours of community service. He must also pay his victim £2,500 compensation.
Recorder Nicholas Rowland heard that Hernandez-Sanchez had been banned from city centre pubs for a year following the incident.
Passing sentence he told him: “Mr Stubbs’ Army training was interrupted.
He wanted to box for the Army and now he cannot do that.”
He accepted, though, that the incident had not been premeditated.