Mariano Rivera
Credit: Jim McIsaac / Getty Images

The Yankees legend has the most regular-season saves (652) and postseason saves (42) in MLB history, as well as the best postseason ERA (0.70). Though he missed most of 2012 with a torn ACL, that was his first trip to the disabled list since 2003. The 43-year-old closer was the oldest active MLB player this past season, which is absolutely amazing for a pitcher.

"To pitch over a long amount of time without injury to your shoulder or elbow is really quite unique," Williams says. "Your mechanics have to be so in tune and perfect that you don't put an inordinate amount of stress to either one of those joints in an action which is inherently stressful."