Now that we’ve had an introduction to weighted on-base average (wOBA), I want to expand on another statistic we can use to contextualize hitting performance: xwOBA, or expected weighted on-base average. If you haven’t read the wOBA article yet, start there first.
xwOBA is calculated using two physics metrics on batted balls: exit velocity and launch angle. Sprint Speed is sometimes a third metric used in calculations, but only in situations where a runner’s speed factors into whether he is safe or out. One example is weakly hit ground balls where the runner relies on his speed to reach base. To calculate xwOBA, every batted ball is given a single, double, triple or home run probability based on the results of other batted balls and their exit velocities and launch angles. xwOBA is then calculated assuming a batted ball resulted in a specific hit outcome.
wOBA and xwOBA differ in that wOBA is based on the actual outcome of a batted ball and xwOBA is based on the expected outcome using the assumptions of exit velocity and launch angle. xwOBA is based on the quality of contact a hitter makes and removes the defense from the equation because a hitter has no control over what happens to a batted ball after it’s in play. xwOBA is best used to compare contact profiles between players.
Comparing a player’s wOBA vs. xwOBA can tell us how “lucky or unlucky” a hitter’s outcomes are. If wOBA > xwOBA, his actual outcomes are better than what we would expect based on the exit velocities and launch angles of his batted balls. This tells us the hitter has had a little luck in reaching base on batted balls we wouldn’t expect to have a high probability of success. And on the flip side if wOBA < xwOBA, the hitter has been unlucky in that he is hitting the ball hard but not having the on-base successes we would expect based on that hard contact. Let’s take a look at the unluckiest hitters in baseball in 2021. Carlos Santana of the Kansas City Royals was the league’s unluckiest hitter with a “poor” level wOBA of .294 when his contact profile tells us he should have been in the average to above-average zone at .334. Freddie Freeman and Jorge Soler, who both found new homes as free agents this spring, also find themselves in the top ten unluckiest hitters list.
Randy Arozarena of the Tampa Bay Rays tops the list of the ten luckiest hitters in the 2021 campaign. Marcus Semien, who just signed a 7 year $175M contract with the Texas Rangers, was near the top of this list last season.
As for the 2021 Cubs? Backup catcher Robinson Chirinos was the luckiest Cubs hitter with actual outcomes 0.050 points higher than his expected. Rafael Ortega was a great story in 2021. He’s earned his opportunity on the 2022 roster it’s possible his 2021 results were a little better than we’d expect based on his contact profile. Matt Duffy finished right around league-average and Willson Contreras finished above-average. David Bote was the unluckiest of Cubs in 2021. His actual outcomes were in the “awful” realm, but even his xwOBA was still below average. Two of the top three ”luckiest” hitters from last season aren’t on the Cubs roster in 2022.
The 368 Project 