Family and friends of Mitchell Cook held a candlelight vigil on the football field at Canyon High School Saturday night.
Cook collapsed Wednesday during warm-ups for the school's freshman team.
Family members say the teen always marched to the beat of his own drum.
"Understand how fragile life is, because I can tell you this is going to be the toughest time of my life coming up," said the boy's father, Jim Cook.
Cook's family says the teen did have a heart condition, but it wasn't considered life-threatening.
An autopsy is expected to determine the cause of death.