Sinclair had to be pulled away by other patrons.
He mistakenly believed the victim had wanted to "smash him" so he punched him first.
The victim suffered multiple fractures to his eye socket and a gash on his head.
Sinclair, and his mother who was sitting in the public gallery, began to cry as details of the attack were read out to the court.
It is the second time Sinclair has been sent to prison for such an offence.
in 2009 he was sentenced to two years in jail for injuring with intent to cause grievous bodily harm.
Defence lawyer Stephanie Burlace said Sinclair had tried to make some serious changes in his life since his release from prison, including moving out of the area and cutting out alcohol almost completely.
This instance was the first time in a long time he had drunk too much and gone out, she said.
Judge Matheson said Sinclair was a dedicated and respected member of a martial arts club, which made the offending worse given the ethical standards he would have been taught there.