Baseball Smarter: What is xwOBA, or wOBAcon? And No, We Didn't Make That Last One Up

Baseball is really hard. Everyone who has played or watched some level of baseball has heard that even the greatest players failed 7 times out of 10. While a massive oversimplification, this has come to be a rallying cry of sorts, used by, for lack of a better term, failures. You never hear this after a positive event; it always follows some sort of negative event and is meant to put an emphasis on how difficult baseball is. 

So we know that in baseball, you’ll fail a lot. Failure, in itself, really is not all that enjoyable. Most people try to avoid failure. They prepare; their process is good, and they control everything they can. And yet, failure still comes frequently. It is why you constantly hear players talk about the process and not the results; they talk about controlling what they can. If process is so important, shouldn’t credit be given for good process?   

In the previous article, I explained what wOBA is and why it is such a useful metric. In this article, we will take it one step further. We will add letters and make acronyms that are even more fun to say! In baseball metrics, x simply stands for expected. So while wOBA explains the results, xwOBA sheds more light on the process.   

Each batted ball has an exit velocity and a launch angle, no matter how much a certain FOX announcer complains. Using the combination of how hard the ball was hit (exit velocity) and whether it was hit in the air or on the ground (launch angle) tells us how likely a ball was to be a hit, regardless of the result. The harder a ball is hit, the more difficult it is for the defense to make the play. Line drives are harder for a defense to make a play on than groundballs and fly balls. Makes sense! With this information, it seems obvious that hitters want to try to hit line drives as hard as they can. We should find a way to reward them for that! This is what xwOBA does.      

So why is xwOBA valuable then? Because life is not fair. Sometimes, hitters hit a 110 mph line drive (good process!), and it gets caught (bad result!). Sometimes, hitters hit a ball 70 mph while breaking their bat (bad process!) and wind up on 2nd base (good result!). If we want to focus on the process and control what we can, xwOBA is the way.

Luck always plays an outsized role in baseball, and xwOBA is just one way to look at luck’s impact. Once the ball leaves a pitcher’s hand or the hitter’s bat, he has no control over what happens next. 

Batting average on balls in play (BABIP) has generally been used to measure luck. It removes strikeouts, walks, and home runs. Removing the “three true outcomes” that don’t involve the defense tells you how often the defense made the play. A player with a BABIP significantly over .300 was considered lucky, whereas one significantly lower was unlucky. In the same way we can get more accurate OPS with wOBA, you can get a more accurate version of BABIP with wOBAcon, or weighted on base on contact. Plus, you get to think of bacon. Win-win! 

wOBAcon tells you how much value a hitter provided when he put the ball in play. A relative of BABIP, wOBAcon does two huge things differently. First, it includes the value of every batted ball in each situation, not just whether it was a hit or not, similar to wOBA. Secondly, it does not exclude home runs as BABIP does. This is good! Just because it goes over the fence doesn’t mean the ball wasn’t put in play. 

The best players in baseball will run a wOBAcon near or over .500, similar to slugging percentage. 

xwOBAcon has the same relationship to wOBAcon as xwOBA does to wOBA. It focuses on the inputs and not the outputs, so as to give a process-based number instead of focusing solely on results.