Raul Alvarez Jr., 16, was taken to Providence St. Joseph Medical Center on July 27 around 6:45 p.m. and died about an hour later.
He was sparring at Pullman's Gym at 4320 W. Magnolia Blvd., said Burbank police Sgt. Darin Ryburn.
"He complained of pain from light sparring while boxing," Ryburn said. "While at the hospital, the male suddenly went unconscious. All efforts by medical personnel to revive the male were unsuccessful, and he was pronounced dead at the hospital about an hour later."
Alvarez Jr. was wearing protective gear while he sparred, according to the Daily News. The case is being investigated by the District Attorney's office, the publication reports.