At his one-day trial, Matthew Spence, 41, said he was driving around on Sept. 15, looking for his son's bike which was stolen two days before. He spotted a youth sitting on the bike at the skate park outside St. Joseph's school.
He approached the youth and grabbed the bike, gave it back to his son and begin interrogating the youth who had the bike.
Brad Tremblay, 17, who was skateboarding at the time, said he intervened when Spence "manhandled" the youth.
"I tried to get between Mr. Spence and the other kid," he told the court.
Spence told Tremblay to mind his own business and the pair began arguing. At one point Spence shoved Tremblay away.
Tremblay threatened to call the police. Spence offered Tremblay his own cell phone to use. Spence then started back towards his truck.
The court heard that a crowd of eight to 10 youths followed Spence and at one point somebody said "if we all rush him at once we can all take him down."
Spence said he turned around and warned them against fighting him. Spence got back to his truck but vaulted back over the fence into the skate park when somebody threw a rock at his vehicle.
More shouting ensued and Spence shoved Elmehdi Sadki, 15. Sadki testified that Spence's hit him in the eye, which left it bloodshot for a week.
Defence lawyer Arthur Von Kursell argued that Spence acted in self defence and out of fear.
Crown prosecutor Jonathan Burke said that Spence could just left the scene and called police on his cell phone at any time.
Judge Robert Halifax, who called the incident "a circus," gave Spence a $300 fine for each conviction.
The judge dismissed Spence's claim that he acted in self defence.
"Self defence is a necessary force to repel force," he said. "To my mind you had no right to push these youths."
"Anger doesn't justify violence," said Halifax.
In sentencing, Halifax cited a previous assault charge on Spence's record from 11 years ago.