CCTV cameras filmed a man throwing a flurry of punches in Grantham town centre while a crowd of around 30 looked on.
Gino Angeloni of Dysart Road, Grantham, admitted a public order offence following the incident which took place in the early hours of July 7 in Westgate, Grantham.
The court heard Angeloni, 19, had initially been the victim of an assault which was also captured on CCTV.
However, Angeloni then went on the attack himself, assaulting a third man. He began throwing punches outside Fabric Warehouse before pursuing the back-pedalling victim into the road where he landed more strikes.
Angeloni threw his final punches once across the road before the victim left the scene.
Julian Sheen, defending, said: “His recollection of the matter was that he was assaulted and that is quite clear. You can see he is retreating.
“But there came a point where he had had enough and he went way beyond self-defence.
“He regrets that and is ashamed of what happened.”
Mr Sheen said the incident began when Angeloni was “set upon” by another male who was not charged in relation to the incident.
Mr Sheen added: “It went on from there and he entirely accepts his involvement and accepts he lost control to a certain extent and must face the music.”
Angeloni was fined £135 and must pay costs of £85.
Chair of magistrates George Hoyles said: “We have watched the video twice. It looked as if the first instance was a general flap around by everybody and then you lost your sense of direction and charged in fighting.”