A Sheffield bar manager was punched in the face by a customer who raced away down West Street following the unprovoked attack.
Gary Sinclair, owner of Maggie May's on Trippet Lane, said his bar manager was attacked as he welcomed customers inside on Saturday night.
The man reportedly attacked the bar manager as he and his friends were leaving the club at around 11.30pm, leaving him with a badly damaged cheek bone.
However, the man then quickly fled down West Street before door staff could intervene.
Mr Sinclair is now appealing for information on identifying the 'scumbag' responsible and has offered a £200 reward for his name.
He said: "Our manager was standing by the door of the bar welcoming customers when the group of lads left.
"Then, the last one of the group took a swing at him and smashed his fist into the face of the bar manager, damaging his cheek bone.
"He was shocked, we all were. This is the first time in six years where a member of staff has been assaulted.
"We are a very safe bar. I can count on one hand the number of incidents we've had in the past five or six years. We are not a trouble hot spot.
"I don't know what went through the man's head. It's an upsetting part of what was otherwise a brilliant weekend."
Mr Sinclair said he has been overwhelmed by the response in Facebook, with his post being shared more than 3,000 times.
Call 101 with any information. South Yorkshire Police has been approached for a comment.