2020 Forecast — Starting Pitcher K% Surgers

Three years ago, I shared an updated version of my pitcher xK% metric, which correlated strongly with actual strikeout rate, given its 0.931 R-squared. While some of my other xMetrics I calculate and then use them to serve as a historical guide to assist in my Pod Projection forecasts, I actually project the underlying components of xK% myself and the vast majority of the time, keep the projected strikeout rate those components spit out. There are instances where I do change the forecast though, as some pitchers have a history of outperforming or underperforming their xK% marks, for whatever reason. Anyhow, let’s discuss four starting pitchers who posted xK% marks above their actual marks, hinting at some upside this year.

Justus Sheffield was a former top prospect with the Yankees and enjoyed somewhat of an extended look for the first time in a Mariners uniform. The outward ERA of 5.50, gruesome WHIP of 1.72, partly driven by a double digit walk rate, won’t get many excited. But there actually is a lot to like here.

He generated lots of swinging strikes, thanks to an elite slider, while his changeup also induced whiffs at a mid-teens rate. The fastball wasn’t any good, which is definitely a concern. But given his strike type components, Sheffield deserved a much higher strikeout rate during his longest cup of coffee so far. He’s the perfect post-hype cheap speculation, regardless of league format. If he could maintain his newfound ground ball tendency, I’m even more intrigued.

Zach Plesac wasn’t on anyone’s radar heading into the season, but 10 excellent minor league starts got the Indians attention and earned him a promotion, where he posted solid surface results. While I could point to his massive SIERA outperformance, which screams downside in 2020, I’ll ignore that for now and just focus on his strikeout potential. He wasn’t particularly strong in generating called or swinging strikes, so his above-20% xK% was mostly driven by a better than average foul strike rate. That’s not exactly the type of strike you want propping up your strikeout rate.

That said, his slider generated an above average SwStk%, while his changeup was marginally below average, but not terrible. You would think with a fastball averaging 94 MPH and peaked at 97, he could must a higher SwStk% on the pitch than 6.1%. His curve, though not thrown much, was awful at inducing swinging strikes, so perhaps he would be better served dropping the pitch for his two better secondaries.

I talked about Patrick Sandoval a tiny bit in my LABR recap (and Sheffield too!), and now that the Angels aren’t getting Ross Stripling, he remains a strong candidate to open the season in the Angels rotation. His swinging strike rate was superb, thanks to a devastating changeup, solid slider, and acceptable curve. While I certainly wouldn’t be betting on a strikeout rate over 27% if he remains a starter all season, his appearance here does validate his whifftastic stuff.

I was so excited when Dylan Bundy signed with the Angels, but then was saddened when I completed his projection and realized he’s still not shallow mixed league worthy. Remember in the intro when I warned of players consistently over- or underperforming their xK% marks. Bundy is one of those…in the underperforming camp. In three of four seasons, he has underperformed his xK% mark by at least 2%. That doesn’t sound meaningful, but if you have look at these numbers as much as I have, you would realize it is.

So for whatever reason, Bundy simply cannot translate his strike type rates into strikeouts. It’s just another way he has been a disappointment. But maybe the move to Anaheim will spark a transformation. I’d be happy to roster him, but I’m not paying a price expecting a breakout.