2020 Forecast — Starting Pitcher K% Decliners

Yesterday, I used my pitcher xK% equation to highlight four starting pitchers whose underlying skills suggested a dramatically higher strikeout rate than actually posted, hinting at upside this year if the pitcher could maintain those skills. Today, let’s talk about the starting pitchers who most outperformed their xK% marks, heightening the risk of a decline this season, absent an improvement in underlying skills.

We had been waiting, and waiting, and waiting for Tyler Glasnow to finally live up to his former prospect glory and apparently all it took was a move to the Rays for him to realize his potential. His breakout was cut short by a forearm injury, but the key here was a major improvement in walk rate (finally!) and more than halving his HR/FB rate from well above league average to significantly below it. This season, he sustained his strikeout rate gain achieved in 2018, and took it up a notch higher to finish above 30%.

Unfortunately, xK% doesn’t believe his strikeout rate surge actually matches the marginal skills improvements he showed. In fact, his swinging strike rate (the Baseball-Reference version using strikes as the denominator) actually declined. While his xK% was higher than his 2018 mark by 1.8%, what drove that increase was primarily a boost in called strike rate. That’s not as sustainable a skill as swinging strike rate, so it doesn’t make me optimistic this is a new level of performance. It’s rare to find a pitcher who is around the league average at inducing swinging strikes post a strikeout rate above 30%. While overall I’m a fan of his, I think his 2019 performance has made him massively overvalued and also his price seemingly ignores the risk of coming back from injury.

Word is that Glasnow has scrapped his changeup and is working on a splitter as his new third pitch. The funny thing is he barely ever threw the changeup, so it won’t matter at all unless he cuts down on his four-seamer in favor of the new splitter. If he could master the pitch, that could result in a skill-fueled strikeout rate over 30%, rather than a luck-fueled one.

You probably didn’t need an equation to tell you that Gerrit Cole was likely to regress from his absurd 39.9% strikeout rate last season. That was actually the highest strikeout rate among qualified pitchers in a season for as far back as FanGraphs data goes back! Perhaps rather than nod that he did indeed overperform, tip your cap as that xK% nearly backs up his performance. He posted the highest xK% of any starting pitcher season on my spreadsheet, which goes back to 2011. Amazing. He didn’t even need to bother getting called or foul strikes, it was all about pumping strikes and then inducing whiffs.

Quietly, Aaron Civale came out of nowhere to enjoy a solid Indians debut…on the surface. Underneath the hood, though, is some scary stuff. Though he didn’t end up being much of a strikeout pitcher, Civale actually deserved an even worse rate than the already below average mark he posted. His problem was two-fold — while he was right around the league average at generating called and foul strikes, he was terrible at inducing swinging strikes. He also struggled with throwing strikes to begin with.

What’s interesting about Civale is that all of his non-cut fastballs generated double digit SwStk% marks. That’s pretty amazing, especially when we know he was awful at inducing whiffs overall. How is that possible? Because his sinker generated a paltry 2.3% SwStk%, while his four-seamer (only thrown 3.1% of the time) generated literally 0 swinging strikes. It’s not like the sinker was great at inducing grounders, as it’s grounder rate was just 48.5%. If I were him, I’d try being cutter-first and then using the rest of his arsenal, scrapping the sinker and four-seamer. But for now, I’m not interested.

Frankie Montas is the second former top prospect on this list to enjoy a small sample breakout. Unlike Glasnow, his season wasn’t cut short by injury, but rather for testing positive for a banned substance. Part of the driver of his breakout was a spike in strikeout rate, a really big spike from 15.2% in 2018 to 26.1%. But xK% is only buying part of that surge.

His swinging strike rate was barely above league average, despite the fact he threw a slider that generated an average rate of whiffs, along with an excellent splitter, inducing a SwStk% over 20%. That’s because he threw his sinker most frequently, which was the least whiffiest pitch for him, as it is for the majority of those who throw it. It also generated a grounder rate below 50% and allowed by far the worst wOBA. Sounds like he should back off the pitch, like Civale should. Like Glasnow, I like this skill set and thinks there are changes he could make to legitimize his 2019 strikeout rate, but without any changes, regression is coming.