He was rushed to Kings County Hospital, where he was pronounced dead.
Officials say Marion was a junior at the Wingate Educational Campus, a group of high schools located several blocks from the tennis courts.
Eyewitness News is told he was practicing with his high school's boys' tennis coach at the time of the tragedy.
The Medical Examiner is conducting an autopsy today to determine the cause of death.
Meanwhile, grief counselors are at the high school today.
The Wingate Educational Campus boys' varsity tennis team has a 6-1 record so far this year.
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