Baseball's playoffs are the great equalizer. The team that wins isn't always the best team; rather, it's the team that gets the biggest contributions from the most unlikely places that advances to the next round of the postseason.
That hasn't necessarily been the case in 2013, as the argument could be made that the two best teams in the game—the Boston Red Sox and the St. Louis Cardinals—are exactly where they're supposed to be, playing for the sport's ultimate prize: a World Series championship.
While we often think of X-factors as only being players who seemingly come out of nowhere to perform at an incredibly high level, that's simply not always true. Established veterans who have struggled at the plate or on the mound and players returning from injury can also be classified as X-factors—and the 2013 World Series is full of players that fit all three descriptions.
Let's take a look at 10 players—five from each team—who could ultimately be the difference makers when the Red Sox and the Cardinals meet in the Fall Classic for the fourth time in their storied histories.
*Unless otherwise noted, all statistics courtesy of Baseball-Reference.com.