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EAST RUTHERFORD, NJ - NOVEMBER 16:   Chris Borland #50 of the San Francisco 49ers celebrates after a tackle against the New York Giants in the fourth quarter at MetLife Stadium on November 16, 2014 in East Rutherford, New Jersey.  (Photo by Al Bello/Getty Images)
EAST RUTHERFORD, NJ - NOVEMBER 16:   Chris Borland #50 of the San Francisco 49ers celebrates after a tackle against the New York Giants in the fourth quarter at MetLife Stadium on November 16, 2014 in East Rutherford, New Jersey.  (Photo by Al Bello/Getty Images)

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NFL rookie retires over brain injury concerns

CNN's Jake Tapper talks with Chris Kluwe about the NFL's concussion crisis and Chris Borland's decision to retire at 24 over fears of brain injury.

NFL rookie retires over brain injury concerns

CNN's Jake Tapper talks with Chris Kluwe about the NFL's concussion crisis and Chris Borland's decision to retire at 24 over fears of brain injury.