Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: San Francisco 49ers player Chris Borland, a leading rookie last season, is retiring from the NFL at age 24 over health concerns related to repeated head trauma, ESPN and the team said on Monday. ESPN reported he was retiring over health concerns related to head trauma, an issue that has rattled the league and prompted a massive lawsuit against the NFL. 'I just honestly want to do what's best for my health,' Borland told ESPN's Outside the Lines. 'From what I've researched and what I've experienced, I don't think it's worth the risk.' He continued: 'I just want to live a long, healthy life, and I don't want to have any neurological diseases or die younger than I would otherwise.'Chris Borland, a leading rookie in 2014, turned down four-year, $3million contract'From what I've researched and what I've experienced, I don't think it's worth the risk,' he saidThe linebacker had two concussions prior to making his announcementA lawsuit filed in 2012 contended that NFL hid dangers of brain injury among players while profiting from sport's violent physical contact 
 Question:He becomes the most prominent _ player to turn his back on a rich contract, a four-year deal worth just under $3million in Borland's case, over concerns about brain injuries.

NFL