A Ford worker punched another man during a night out with his family after he was set upon by a group of people.
William George Watkins, 22, of Knareborough Drive, Grantham, admitted using threatening, abusive or insulting words or behaviour in the Market Place in Grantham on December 21 last year.
Prosecuting, Daniel Pietryka said it was just after 2am whan a police officer saw Watkins and another man throw punches.
Watkins had fallen to the floor and he was detained. The other male ran away but was detained later.
Mr Pietryka said Watkins was out for a night with family and friends and was assaulted by an unknown man.
He had chased this male and then returned to his family when another man started shouting in his face.
Watkins believed either he or his sister were going to be hit and he accepted there were punches thrown.
He had said his actions were in self-defence.
The court heard that Watkins had been drinking that night. He had suffered a cut to his left eye and there was swelling and bruising.
Watkins, who was not represented, said: “It was a silly drunken act. There was no excuse for it. I did not intend for it to happen. I was standing with my sister when three people approached me and punched me. I thought the right thing to do was to chase them away. I was stupid. I am sorry.”
Watkins, who told the court he painted cars at Ford, was fined £200 and ordered to pay £85 costs and a £20 victim surcharge.