A Mississauga high school student was found guilty of manslaughter today in the death of a rival player during a rugby game.

The teen, now 18, was visibly upset – as were family members – after Justice Bruce Duncan rendered his decision in a Brampton courtroom.

His mother hugged him as he sat forlorn, his head down, at a table at the front of the packed Brampton courtroom.

Justice Bruce Duncan decided his actions on the Lorne Park Secondary School playing field in 2007 caused the death of Manny Castillo.

The convicted teen, a major junior hockey player with an Ontario Hockey League team, remains on bail. He'll return to court July 6 for his sentencing hearing.

For now, his identity remains protected by Canada's youth laws. But that could change.

Crown prosecutor John Raftery said he's considering asking for an adult sentence.

Duncan, however, told the Crown after rendering his decision that he didn't believe - from what he heard - that an adult sentence was appropriate.

There is no minimum sentence for manslaughter. He faces a maximum three years sentence if sentenced as a youth. Life in prison is the maximum adult sentence but it's unlikely in this case, even if an adult sentence is rendered.

Castillo's parents declined to comment. Their thoughts will be given when they file their victim impact statements at their 15-year-old son's killer's sentencing hearing.

They and the convicted teen and his mother were taken to an underground level of the courthouse and driven away instead of walking out the front door.

In rendering his decision, Justice Duncan rejected the defendant's self-defence claim that he only pushed Castillo to the ground to get out of a choking headlock during continuous play on May 9, 2007.

"The defendant intentionally applied force that was outside the rules of the game or any standard by which the game is played," Duncan said. "Manny did not explicitly consent to that force.

"I'm satisfied beyond any doubt no consent can be implied.

"There was no justification in self defence. Accordingly, the defendant committed an assault, an unlawful act. That unlawful act caused death. The defendant is therefore guilty of manslaughter."

Defence lawyers Lisa White and Calvin Barry had suggested Castillo knew he was playing in a physical game and that he accepted the dangers of the contact sport when he entered the field to play for his Lorne Park team that tragic day.

But Duncan rejected her assertion.

He described what the defendant did as being a "sucker tackle" and said at its "highest" it was done out of retaliation, not self defence.

Although he believed evidence indicated Castillo likely did place the defendant in a headlock, it was only for a brief few seconds and it ended before he was tackled to the hard playing surface.

Castillo died from a serious head injury a few days after the incident.

Crown prosecutor John Raftery said during the two-week trial that the accused committed manslaughter when he lifted Castillo into the air, his feet facing upwards, and drove him head first into the ground.

He took the stand in his own defence and claimed he reacted aggressively to get out of a headlock applied by Castillo, who was pushed, not dumped, to the dirt.

He said it was an unlawful assault outside the rules of the game.

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Raftery insisted in his closing remarks that the deadly move was separate and away from the normal play on the field and the ball was nowhere near them.

Following the critical play, Castillo lay motionless, and was dying from severe head and spinal cord injuries.

During the trial, various witnesses – including players, coaches, the referee, parents and rugby experts – gave conflicting accounts of what they saw.

Some said they saw Castillo put the defendant into a headlock and others didn't. Some said the play had already stopped at the time and others didn't. Some witnesses saw Castillo driven to the ground, others said they saw him fall gently over the shoulder of the accused.

As for the convicted teen, he testified that he fell on top of Castillo when he wrestled his way out of a headlock. He said he had panicked because he couldn't breathe and denied intentionally hurting the opposing player. He said he was unaware Castillo was injured when they both fell to the ground.

He never lifted him up or drove him head-first into the ground or boasted about it afterwards, as Crown witnesses said.

Duncan found it was a fact that the defendant was put in a headlock but only for a few brief seconds. He didn't believe he was ever in a choke hold and if he was, he never just used his hands to take Castillo's arms away from him.

He didn't believe the fatal assault occurred during a continuous play.

He found there was as a "hiatus" or break between the headlock and the assaulted tackle.

"I'm satisfied beyond any doubt the headlock ended before the tackle and it ceased to have any legal significance," Duncan said.

He found the defendant tackled Castillo from some distance.

He said the intentional force applied by the defendant was not within the rules of the game,"

Castillo was later declared brain dead in hospital. He also sustained a bruised spinal cord, which would have been fatal had paramedics not attended. The spinal cord injury occurred when his neck was flexed forward – not backward – beyond its range of motion, according to a neuropathologist.

Had he survived, Castillo could have been paralyzed.