The 15-year-old black belt thought he was doing his tormentor a favour when he elected to fight back with his weaker left hand.

He had heard his white classmate throw an angry racial slur in his direction after an argument during a gym class game of speedball, and now the student was shoving him backward, refusing to retract the smear.

The white student swung first, hitting the 15-year-old with a punch to the mouth.

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The 15-year-old heard his father's voice running through his head: Fight only as a last resort, only in self-defence, only if given no choice, and only with the left hand.

His swing was short and compact, a left-handed dart that hit the white student square on the nose.

The nose broke under his fist, igniting a sequence of events - from arrest to suspension to possible expulsion - that has left the Asian student and his family wondering whether they are welcome in this small, rural and mostly white community north of Toronto, one that has been touched by anti-Asian attacks in the past.

The 15-year-old, the only person charged in connection with the April 21 school fight, faces one count of assault causing bodily harm.

But a remarkable thing happened this week.

On Monday, 400 of his fellow students, wearing black in solidarity and carrying signs of support, walked out of Keswick High School to rally in protest in front of their school.

Organizer Mathew Winch, a Grade 12 student, said the school has fewer than 10 Asian students, but everyone wanted to stand up against bullying and racism. The story even hit the front page of local newspapers.

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After the public outcry, the York Regional Police hate crimes unit reopened the case. Although the other student has not been charged, further charges are possible, a spokesman said yesterday.

The case is particularly sensitive because of a series of attacks on Asian fishermen in the same area in 2007 - given the name "nipper tipping" by locals - which led to a high-profile investigation by the Ontario Human Rights Commission.

Five such cases in 2007, ranging from violent car chases to fishermen on piers being pushed into the water, led to criminal charges. As a result of the publicity, many other Asian anglers came forward to say they had been abused or harassed while fishing in the Lake Simcoe area.

The Asian boy's father is a martial-arts master who trained with the Korean national team. He brought his family to Canada in 2004.

They settled in Keswick in 2006, and his son, who is still learning English, has studied hard to become a top student.

He proudly showed off a report card with a 90-per-cent average. The boy has struggled a little socially, his parents said, which makes the outpouring of support from his classmates all the more remarkable.

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"It's the first time in my life I ever fought someone. I've been trained not to attack. It's total self-defence," the boy said. "I felt sorry because I broke his nose, but I can say he deserved it because he called me the racial comment. He started the fight, he punched me first."

He said the boy called him a "fucking Chinese," a comment he instantly knew was far from a joke.

"It's upsetting," he said. "I don't know how better to tell it."

For the moment, both students are suspended from Keswick High School, but the Asian student's parents have been told he could be expelled and forced to find a new school.

They are shocked and saddened by the ordeal.

The day after the fight, an older cousin of their son's antagonist approached him in the school cafeteria and uttered a similar slur, compounding their sense of despair.

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"He said, 'You punched my cousin you Chinese fuck,' " the 15-year-old said. That student was overheard by a teacher and suspended.

His father explains that the easiest course would be to move somewhere else and get a fresh start for his son. But he can't do it.

"I don't want to run away. If another Asian kid comes to this school, what happens to him? Will he run into problems? Will they think they can just kick him out? I don't want to set that example," he said.

"Personally, for my kid, I should move. But as a Canadian I cannot move."