8) Adrian Peterson, Minnesota Vikings running back: Peterson is free agency's Rorschach test. He has played in just 20 games in the past three years, but he's bringing fresh legs and extra motivation to his next team. He eked out 1.9 yards per carry last year, but can the 2015 NFL rushing leader be blamed for a microscopic sample size and a pathetic offensive line? On the wrong side of age 30, he's still an obvious candidate for the best age-32 season in history.