As the group left they began to yell homophobic slurs at patrons who were entering the bar, and even threw a can of alcohol at one.
When Mr Mawhinney tried to intervene to stop the attack, he was hit in the head by Sherman, Ms Handcock said.
As a result he received bruising and a scratch to his face.
In his victim impact statement, Mr Mawhinney said on the night of the attack he believed the group was on a "homophobic tirade".
He says after being hit he was unable to smile, laugh or chew food for some time, and often jumped when he heard loud noises as a result of the attack.
'There have been a number of times when rougher looking people have come into the bar and I am so on edge.
"This has put fear in people... and it will put many people off from being who they are."
He said the attack was an example of "outdated hatred and abuse" which was "unacceptable".
Judge Ian Mill said he agreed with Mr Mawhinney's statements, before he remanded Sherman on bail until sentencing on March 25.