He punched his brother to the side of his head and was arrested.
Defence lawyer Virginia Pearson said the fight may have "de-escalated" on its own had the police not arrived.
Ms Pearson said both brothers had been involved but only one had been charged.
"There were no injuries, the [other] brother really didn't wish to pursue matters himself."
Judge Geoffrey Ellis asked if the brothers would be able to reconcile.
"Will you two be able to get over this - have a beer and shake hands?" Judge Ellis said.
He convicted Thornton and gave him a sentence to come up again if called upon in six months.
"I want there to be some breathing space, so everything can calm down.
"Put it behind you and forget it."