When Moneyball was published back in 2003 it taught us the true value of a walk. For decades baseball had been played with the idea that a walk was only the fault of a pitcher. Moneyball changed that. We know realize that the ability to draw a walk is a skill. For a while players who appeared otherwise average, but had a high OBP, were a market inefficiency smart teams sued to gain a competitive advantage. The Red Sox, for instance, used Moneyball concepts in their 2004 World Series run.
Once OBP was properly valued teams tried to find the next Moneyball. In recent years this has included teams placing a greater emphasis on contact skills, fielding ability, and acquiring hard throwing relievers to shorten playoff games. The Royals, for instance, used these concepts to win back to back pennants in 2014 and 2015. But the latest, greatest, baseball stat is a new one altogether. It's called average exit velocity.
In it's simplest terms "avg EV" measures how hard a player hits a ball. The thought is that if a player hits the ball hard then he has a better chance of getting a hit. The stat can also be used for regression analysis. For example, if a player has a high batting average but a low avg EV, there is the chance he is getting lucky with softly hit balls falling in for hits. Likewise, if a player has a batting average below his career norm but a high avg EV, he could be due for a breakout.
It should come as no surprise that when taking a look at the avg EV leaders in 2016 some of the best players in baseball show up, such as Giancarlo Stanton, David Ortiz, and Miguel Cabrera. (BBE stands for batted ball events and represents any batted ball that produces an out, hit, or error). What is cool about the avg EV leaderboard is seeing a name like Christian Yelich up there. Many casual fans may not be familiar with him but he is a 24-year-old outfielder for the Marlins setting career highs in every offensive category this year thanks in part to a high avg EV. As you can tell in the graphic above he ranks 10th in all of baseball in avg EV at 93.4, which is up from the 92.0 mark he posted a season ago. Still it's important to keep in mind that avg EV doesn't tell the whole story. It's not a perfect stat, although it's useful.
The Tampa Bay Rays use avg EV instead of batting average to measure all their hitters. But the stat has become more mainstream since MLB's stat cast system, which uses high resolution cameras and radar equipment to track everything that happens on a baseball field, launched in every MLB ballpark in 2015. Teams had been using some of these new stats for player evaluation prior to 2015 but the recordings are now available to the public. They are working their way into broadcast booths and online message boards. Two parks even have EV readings up in their stadiums, similar to how pitch velocity readings are shown.
More information on statcast and avg EV can be found in this recent SI article. The video below is a great intro on a bunch of stats that MLB Statcast tracks.