Astros Analysis: Examining the unluckiest hitter by xwOBA

Batted ball data from MLB’s Statcast is still relatively new to the analysis scene, but it does provide helpful hints on how a hitter is performing by underlying numbers.

One of the key metrics from Statcast that I find particularly interesting is expected weighted on-base average, otherwise known as xwOBA. Per the definition provided by MLB.com, xwOBA is calculated by using launch angles and exit velocity. Essentially, the metric attempts to measure a hitter’s quality of contact.

Craig Edwards of FanGraphs and Jonathan Judge of Baseball Prospectus within the last six months have released helpful studies on the matter, exclusively in how xBA and xwOBA apply to pitchers in Judge’s own analysis. As noted by Edwards, there is still a learning curve on how to properly utilize the stat. But he does note that the stat appears to hold “some predictive value” for hitters. For this one brief post, I’d liked to examine the one Astros’ hitter who had the “unluckiest” season based on actual wOBA and expected wOBA.

The answer: top prospect Kyle Tucker.

We’re all familiar with Tucker’s lackluster results in 2018. Throughout 72 plate appearances in 28 games, the Astros‘ prospect finished the season with a .141/.236/.203 slash line with a 28 wRC+. Not a great debut based on the surface level stats. But it is wise to look beyond surface level stats and dig deeper to find some positive indications from Tucker’s first look at major league pitching.

Out of all Houston hitters with at least 50 batted ball results, Tucker came in with the lowest wOBA (.206) of any player on the team. He also finished with the most significant discrepancy between his wOBA and xwOBA (-.118).

Table 1. wOBA-xwOBA

wOBA     xwOBA
.208         .326

Based on his quality of contact, Tucker should’ve been a much better hitter than what common metrics show. While 72 plate appearances is a small sample, his .326 xwOBA was the fourth-highest among Houston hitters. If you were to lower the minimum batted ball results to 25, you’d find that Tucker also had the highest average exit velocity (90 MPH) on all plays that ended with an out recorded. When he made contact, the ball wasn’t hit all that soft. Out of all Astros’ hitters with at least 20 plate appearances, Tucker finished the fourth-lowest soft hit percentage (13.7%). There was hard contact. His low .176 BABIP in the majors last season help verify this theory that he just ran into some bad luck.

Although the peripherals show that Tucker should’ve performed better than his actual results, there is a portion of the fan base ready to write him off. That’s not wise as Tucker will likely be a productive major league player, sooner or later. Remember that he will enter his age-22 season by the time spring training rolls around. Sure, he had a 155 wRC+ in the hitter-friendly Pacific League this year, but his results remain impressive. Alas, his future in Houston depends on the outcome of the upcoming offseason based on certain trade rumors. No matter of the uniform he wears, I am expecting good things out of Tucker in the near future.