A 21-year-old has pleaded guilty to using threatening behaviour and words at Grantham bus station on Wharf Road.
Darren Smart of Heathfield Road, Grantham, admitted committing the public order offence on December 18.
Prosecutor Marie Stace described how at 3.20pm the defendant had come out of a shop and seen his girlfriend involved in an altercation.
Angered by this, he ran over with a friend, and recognised the others as a group with whom they had been having an ongoing dispute over some photos.
At the time Smart had his arm in a plaster cast, but he lifted it up at the group and said: ‘This is going to happen to you’, before making more threats that he would get his relatives to attack them.
He also shouted and swore at other people nearby, including someone who was trying to calm the situation down, added Miss Stace.
Defending, Chris Pye-Smith said that it happened after Smart had been to have his haircut, and on exiting the barbers he saw his girlfriend surrounded by three other females.
Although he had been trying to help her, Mr Pye-Smith added: “He accepts that it wasn’t necessary to take that step, and it could have been dealt with in some other way.”
Smart was fined £165, and must also pay £85 in prosecution costs and a £20 victim surcharge.