Joseph Barajas, a 15-year-old high school football player, died three days after injuring in his head in a collision with another player and a month after a concussion in another game.
Hospital officials listed cause of death as "traumatic brain injury."
Barajas, a sophomore at San Jose's Pioneer High School, collapsed on the sidelines Saturday after slamming into another player during a junior varsity game, said Maureen Davidson, spokeswoman for the San Jose Unified School District.
He suffered a blood clot on the brain and had been hospitalized since then.
It was the second time in four weeks that Barajas, who played linebacker and guard, was injured on the field. A concussion sidelined him for weeks until he was cleared by a doctor to resume playing, coach Tim Lugo said.
Concussions are caused when a blow rotates and twists the brain in the skull, damaging brain tissue. They can cause swelling and other damage and in some cases lead to long-term cognitive dysfunction.
An estimated 63,000 high school varsity athletes participating in any of 10 sports suffer a concussion every year, according to a nationwide study published last month in the Journal of the American Medical Association.
It is hard to tell if Barajas' first injury contributed to his death, said Dr. Martin Holland, director of the brain and spinal cord injury program at the University of California, San Francisco.
On Tuesday, the flag was lowered to half staff at Pioneer High School, where principal Ardith Heinrich called Barajas a classy young man. He played tenor sax in the school band and was considered a top student. His twin brother, Christian, also played on the junior varsity football team. Their brother Adrian is a junior.
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