Chris Borland
After an award-winning collegiate career at Wisconsin, linebacker Chris Borland joined the San Francisco 49ers in 2014 and soon worked his way into the starting line-up. However, after just one year in the league, Borland abruptly retired due to rising concerns over CTE and other brain trauma resulting from football, and has since continued to distance himself from the game. In hindsight, Borland’s decision may have been a harbinger of some of the NFL’s more recent early retirements.