Coming off the bench and joining his teammates in a circle for a quick rally cry Monday, his knees buckled and he collapsed, Coach Scott Martin said.
After a trainer offered mouth-to-mouth resuscitation and paramedics could not revive him, Martin died at Riverview Hospital in Red Bank, school district spokeswoman Marianne Kligman said.
"His eyes rolled to the back of his head. He was having some sort of seizure," said Coach Martin, no relation to the deceased.
Martin slimmed down from 290 pounds in his freshman year to 220 by his senior year and had a strong work ethic, his coach said.
The star's mother, Tracy Dixon, and his sister, Serena, attended the scrimmage against Point Pleasant Beach, The (Newark) Star-Ledger noted.
Dixon told the coach her son had never been treated for heart problems, the coach said.