Tarik Skubal Has Found a Groove

Chosen in the ninth round of the 2018 draft, Tarik Skubal had a meteoric rise in prospect pedigree, tearing through the minor leagues in just 145 innings. He allowed just one earned run in 22.1 innings in 2018, then compiled a 2.58 ERA in high A and a 2.13 ERA in Double-A, but what caught the eye of analysts and prospect hounds alike were the strikeout and walk rates. He punched out about 40% of the batters in 2018 versus a walk rate of about 5% and posted strikeout rates of 30.3% and 48.2% in high A and Double-A, respectively, against walk rates of 5.9% and 10.6% in ’19.

Those numbers earned Skubal a place on our 2019 Tigers list before the start of that season, with Eric Longenhagen and Kiley McDaniel noting that he “dominated in pro ball after signing by throwing about 80% fastballs. He’s a ground-up rebuild who had third-round stuff at his best in college.” After he continued to dominate in 2019, Skubal climbed the 2020 version of the list, placing fourth behind three excellent prospects in their own right.

Skubal missed the entirety of the July summer camp last year but showed enough at the alternate site to earn a call-up, making his major league debut on August 18. It didn’t go to plan, though: He struck out a healthy 27.9% of batters with an 8.2% walk rate but also allowed a 72.3% fly ball rate with a 20% HR/FB ratio. That led to an ugly 2.53 HR/9 and a 5.63 ERA over 32 innings.

Unsatisfied with his 2020, Skubal made the pilgrimage to Driveline Baseball over the offseason. There, he first tried to make improvements to his existing changeup, but nixed that in favor of working on a splitter after immediately feeling comfortable with the offering used by his highly-touted teammate, Casey Mize.

Despite the new offspeed pitch, Skubal surrendered a 6.14 ERA in April despite allowing a miniscule .242 BABIP. His walk rate increased from 2020, and he was allowing even more contact in the air. And the splitter was not doing him any favors, with a pedestrian 10.2% SwStr% (the average for a left-handed pitcher’s splitter is 24.5%). He also had no control over the pitch, posting a 33.9% zone rate. Those two factors led to a .539 wOBA allowed on it.

About midway through the month, manager A.J. Hinch mentioned in a postgame press conference that Skubal would throw more breaking pitches going forward at the expense of his new splitter. That wasn’t all; he made a substantial change in terms of fastball usage after his start on the last day of April.

Not only did Skubal get rid of the splitter, but he also brought back the changeup and started to work in a sinker, largely at the expense of his two breaking balls and his four-seamer, which is still his most-used pitch.

The drastic intra-season alteration has not gone unnoticed. And while Skubal’s remodeling was stark, the uptick in performance since his April 30 start is striking.

Skubal has added almost 75% to his strikeout rate and trimmed his walk rate by 47.5% since his pitch mix evolution. Despite a .316 BABIP since the start of May, he has an ERA of 3.78 over that span. That increase in BABIP has not been so bad because he is keeping hitters off the base paths with all the extra strikeouts, but it also makes sense, since he is now inducing groundballs at a much higher rate. Since he went back to the changeup and incorporated the sinker, it’s almost doubled, now sitting at a career-high 40.8%.

Though that still falls a few percentage points below the league mean, it is a massive step forward for Skubal. Groundballs, on average, have a .236 BABIP in 2021 versus .098 for all fly balls. He was allowing an inordinate number of fly balls, which naturally deflated his BABIP. Home runs are also not included in the calculation of BABIP, which meant that his 3.28 HR/9 in April (1.22 is league average) didn’t affect that calculation either. Skubal now has a 1.48 HR/9 — not great, but more palatable.

When you dig deeper into each pitch’s results, it becomes obvious how these improvements came to fruition.

Skubal’s four-seamer is a solid offering relative to other left-handed fastballs, but his curveball fails to generate swings and misses or ground balls despite outlier levels of drop. Given that none of his pitches drop nearly as much as the curve and that none are close to its velocity band, I would think opposing batters must be able to pick it up out of Skubal’s hand. He uses it sparingly (about 8% of his total pitches), but that still might be too often without a further adjustment. The slider, meanwhile, is an above-average offering in terms of swinging strikes but notably is his second-best pitch in terms of getting hitters to put the ball on the ground, a result of deceiving batters with movement derived from seam shifted wake.

The main changes here are the introduction of the sinker and shelving the newly developed splitter in favor of the changeup; those best explain Skubal’s uptick in performance. He has had more success throwing the changeup in the zone (compared to the splitter), which has yielded more swinging strikes (17.8% versus 10.2%) and many more groundballs (34.8% to 10%). Speaking of groundballs, Skubal’s sinker gets almost three inches more drop than his peers, enabling him to spot it more aggressively in the strike zone on the hands of left-handed hitters, which results in extra whiffs along with weak grounders.

Using my called strike probability model (which I used in a recent post on Zack Greinke), I separated Skubal’s pitches into three bins. Pitches in the first decile in called strike probability were considered easy takes, pitches in the last decile were easy swings, and all other pitches were borderline.

As you can see, swapping the splitter out for the changeup makes swing/take decisions exceedingly more taxing for Skubal’s opposition. The sinker has been his best offering in terms of these borderline decisions, giving him another weapon to put batters in a bind when they step into the box.

Coming off a wanting 2020 debut, Skubal showed a great deal of effort in going to Driveline and adding a new pitch. When that pitch was clearly not working, he was willing to accept the sunk cost and scrap it despite spending valuable time attempting to hone it. And on top of completely turfing the splitter, he also added two new pitches in the middle of a season. Fortunately for Skubal, these adjustments are paying off in spades. He has been excellent since his rough first month, and if he can maintain this level of performance going forward, he should be a stalwart for the next great Tigers club.