An Ontario judge sent out a warning Thursday that the playing field is not a “criminal law-free zone” as he convicted an 18-year-old rugby player of manslaughter for a violent sucker-tackle that caused a rival’s death.

Manny Castillo, 15, died from a head injury just days after he hit his head on the field during a high school rugby game in May 2007.

Justice Bruce Duncan ruled the convicted athlete had no exemption to use deadly force simply because he was participating in a sport known for its testosterone-fuelled aggression.

“The playing field is not a criminal law-free zone. The laws of the land apply in the same way as they do elsewhere,” he told the court in handing down his verdict.

The now 18-year-old athlete, who also played top-rank hockey, “committed an assault, an unlawful act,” Duncan said.

“That unlawful act caused death. The defendant is therefore guilty of manslaughter.”

Court heard the assault came in the dying seconds of a rugby match on the Lorne Park Secondary School field in Mississauga.