The Statcast revolution is well under way. Tracking every player, every batter, and almost every single batted ball provides a wealth of data for people to work with, and that data is slowing being converted into a useful form. The newest metric to debut is “expected wOBA”, or xwOBA, and it’s another step toward better understanding of baseball.
As the name makes clear, xwOBA is based on wOBA, which stands for “weighted on-base average” and is a catch-all offensive statistic. While batting average and regular on-base percentage treat every time a batter gets a hit or reaches base equally, wOBA credits a hitter based no how much each type of hit or method of reaching base is worth.
If wOBA is meant to be add accuracy to OBP or AVG by evaluating batting events with more precision, xwOBA is meant to add accuracy to wOBA in much the same way. Instead of treating all singles as equal, and all home runs as equal, xwOBA uses the new Statcast tracking to assign every batted ball a likelihood of turning into a single, double, triple, home run, or out, and gives credit to the batter based on that probability. Instead of treating a pop up that drops in behind second base and goes for a single as equivalent to a screaming liner that the center fielder just barely cuts off before it reaches the gap and that also goes for a single, xwOBA looks at what usually happens to balls hit at that launch angle and velocity.
Now, there are lots of reasons to be skeptical of Statcast. It still isn’t tracking every pitch and/or batted ball, though xwOBA does its best to work around that. The new metric doesn’t incorporate park factors, so it treats a long fly ball to left in Fenway Park just like a long fly ball anywhere else, even though that kind of ball is often a double in Boston. But there is a lot of potential for accuracy and precision here, and that’s very exciting.
So with that in mind, who are the early leaders in this new metric?
2017 xwOBA Leaders
Unsurprisingly, a bunch of really good hitters, or at least a bunch of hitters who have been really good thus far in 2017. Indeed, almost nobody on the list is a surprise. Freddie Freeman has tapped into his power stroke more than ever before, Aaron Judge has been making lots of news in his first full season, and Eric Thames... well, you know about Eric Thames now.
In one way, this list is almost disappointing; there’s nobody on here who is getting totally screwed by the traditional ways of measuring offense, and who xwOBA reveals as a secret offensive superstar. Once of the criticisms of another newish Statcast metric, “Barrels,” is that it doesn’t actually do anything above and beyond the currently existing metrics, and it’s possible that xwOBA falls into that trap as well. Maybe the kind of balls that make regular wOBA less reflective of a hitter’s ability — the screamers to the gap that are somehow caught, or ball hit over the fence but pulled back by an enterprising outfielder — are just too infrequent to make adjusting for them very informative.
We’ll be digging into those questions a bit more later in the week, but for, it suffices to say that xwOBA is certainly picking up on hitting ability. It certainly won’t be the last new toy Statcast presents us with, but it’s the latest, and that makes it worth our attention.