A 14-year-old football player collapsed during practice at Mount Saint Michael Academy Tuesday and later died, police say.

Dominick Bess, of Baychester, was taking part in cardio drills around 8:45 a.m., when emergency responders say he went into cardiac arrest. After he fell, school staff tried to resuscitate him and paramedics arrived to rush him to Montefiore Medical Center, where he was pronounced dead.

A source at the school says the students were exercising outside in shorts and T-shirts without pads – training that officials say is not rigorous. Authorities say they were not immediately sure whether the boy had a pre-existing condition. It was his first day of practice.

Mourners paid their respects at his family home in Baychester. An uncle says Dominick was outgoing, loving and an exceptional student. He had received a scholarship to attend the private Catholic school and would have started classes there this upcoming semester. His mother was too upset to speak with News 12 on camera.

The school released a statement offering "heartfelt thoughts and prayers" to Dominick's family, friends and teammates.

It's unclear whether heat or exhaustion played a role in Dominick's death, but there was a heat advisory in effect in the Bronx from noon to 6 p.m. School officials say practice was earlier in the morning. The medical examiner will determine an official cause of death.