Two men were inside a car when a hammer wielding attacker smashed the windscreen and passenger window.
Ian Verroken, described as having “significant mental health problems”, believed one of the pair had pushed his mother’s elderly neighbour.
But the car’s owner, Wayne Reeve, and friend George Medford denied doing any such thing, Spalding magistrates heard.
The incident happened in Riverbank, Spalding, on October 30.
Jim Clare, prosecuting, said Mr Reeve and Mr Medford were having a cigarette and chatting when Mr Reeve received a phone call from his boss asking if he could work for a few hours.
He started the car but then saw Verroken standing on the road with his right hand behind his back.
Verroken shouted “stop” and Mr Reeve described Verroken’s face as “angry and determined”.
Mr Reeve stopped the car and Verroken swung the hammer at the upper left corner of the windscreen, which started to fall away, and swung it again at the passenger window, causing glass to smash over Mr Medford.
In a statement to police, Mr Reeve described how frightened he and Mr Medford were.
Mr Reeve continued: “We were only sitting smoking and chatting and didn’t speak to or upset any other person.”
Verroken (32), of Alcorn Green, Fishtoft, near Boston, was conditionally discharged for a year and ordered to pay £85 costs with £500 compensation.
Solicitor Rachel Stevens, mitigating, said Verroken has significant mental health problems and was in court with his sisters, who are part of a team of people who provide him with full-time care.
Verroken was visiting his mother when an elderly neighbour of hers was pushed and swung the hammer “as an angry reaction to what he witnessed occurring”.
She said Verroken realised it was not the right thing to do.