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BERKELEY, Calif. -- San Francisco 49ers linebacker Chris Borland, one of the NFL's top rookies the past season, told "Outside the Lines" on Monday that he is retiring because of concerns about the long-term effects of repetitive head trauma. Borland, 24, said he notified the 49ers on Friday. He said he made his decision after consulting with family members, concussion researchers, friends and current and former teammates, as well as studying what is known about the relationship between football and neurodegenerative disease. "I just honestly want to do what's best for my health," Borland told "Outside the Lines." "From what I've researched and what I've experienced, I don't think it's worth the risk." Borland becomes the most prominent NFL player to leave the game in his prime because of concerns about brain injuries. More than 70 former players have been diagnosed with progressive neurological disease following their deaths, and numerous studies have shown...