He had a blood clot deep in his brain.
Sumner collapsed on the field while practicing with the Simi Valley Vikings Youth Football Team last Thursday.
He died the next day at a hospital.
It's unclear when or how he sustained the head injury.
Football player's cause of death revealed
SIMI VALLEY, Calif. The L.A. County coroner's office says /*David Sumner*/ died from an acute sudural hematoma due to a head injury.
