Alleged victim Andrew Adams.
Matthew John Blanch, 26, and Christopher James Blanch, 28, were standing in a parking space putting groceries in their car in Goodna's St Ives Shopping Village before the alleged incident.
Ipswich District Court was told Howard Andrew Adams, 43, who was driving his partner to the shops, nosed his vehicle into the space and told the brothers to move.
Crown Prosecutor Noel Needham said the Blanch brothers swore at Mr Adams and told him to leave.
Mr Needham alleged that when Mr Adams got out of his car, Christopher Blanch removed his belt, which had a metal sun or bike cog-shaped buckle, and swung it around.
Mr Adams told the court he thought Christopher Blanch was going to damage his car so he restrained the younger man against it.
Matthew then allegedly punched him from behind, fracturing a bone in his face, and caused him to stumble.
It is alleged Christopher Blanch then swung his belt, hitting Mr Adams in the face.
Christopher Blanch then allegedly spat on Mr Adams' partner at the time, Elizabeth Ann Kennedy, as they left.
It seemed to be a case of "one for the road," Mr Needham said.
Mr Adams and Ms Kennedy managed to write down the Blanchs' car registration plate number and called police.
A doctor gave evidence that Mr Adams suffered a facial fracture under his eye and a cut above his eye which required six stitches.
Defence barrister Ross Summers argued the injuries could have been caused by just one blow.
Matthew Blanch pleaded not guilty to grievous bodily harm over the alleged incident on September 14, 2008.
Christopher Blanch pleaded not guilty to assault occasioning bodily harm while armed and common assault.
Mr Summers said Christopher Blanch denied removing his belt and said he was attacked first by Mr Adams.
He said the brothers only acted in self defence.
Judge Deborah Richards will continue summing up the case this morning before the jury retires.