A jury heard how thug Catterill knocked the innocent victim unconscious as he struck him from behind.
Leeds Crown Court heard the attack took place in the Old Kings Arm pub, Horsforth, Leeds, on April 5 last year as people were enjoyed the Easter Bank Holiday weekend.
Jon Gregg, prosecuting, said the incident took place in the early hours of the morning when Catterill and other men were involved in a fight which was captured on CCTV.
The victim was nothing to do with the disturbance but was hit by Catterill as he walked past.
Mr Gregg told the jury: “(The victim) will not be able to tell you much about what happened because he was knocked unconscious by a dirty blow by this defendant.”
The victim was dragged clear of the disturbance by his friend to prevent further injury.
He had to have a head wound stapled back together as well as suffering the broken jaw.
Mr Gregg said: “The defendant is an easily identifiable man.
“He has a large tattoo sticking to his neck and he has a smaller tattoo under his eye.
“He was identified by those features on the night in question as the man who threw the punch.
“The prosecution say that this defendant acted thoroughly cowardly, thoroughly unlawfully. He hit a man who wasn’t even looking at him and knocked him unconscious.”
Catterill will be sentenced later this month along with two other men who pleaded guilt to assault over their involvement