Mathieu tore his left ACL in December of 2013 at a time where he was a strong contender for the Defensive Rookie of the Year. This season he was one of the top defensive players in the entire league because he does a little bit of everything. He's the ultimate 2015 weapon in the secondary with an ability to play slot cornerback, free safety, strong safety, and linebacker. His instincts and ability to wrap at tacklers near the line of scrimmage is uncanny. ProFootball Focus listed Mathieu as a cornerback, and had him ranked as the top player at his position in the league by far.