The art of sabermetrics—first brought to the mainstream by Michael Lewis’ 2003 book, Moneyball—is, essentially, the math of baseball. Since the book’s publication, a new breed of baseball personnel—such as the Cubs’ Theo Epstein (formerly of the Red Sox) and Boston’s Ben Cherington—have followed in Oakland A’s general manager and Moneyball star Billy Beane’s footsteps, and the way a winning team is built has changed fundamentally.
The most crucial statistic to understanding the sabermetrics revolution is WAR, or wins above replacement. It also might be the most complicated metric to understand. The above video is as simple as possible a breakdown of what the stat means and why it’s important.