Pitchers to File Away by SIERA

These guys might have more in the tank than we've seen.

There are arguments all over right now about how much we should really weigh this season when evaluating players for next year. Do we count it as a pure third of a season? As a half? As a part of a third of a season, given the absurdity of it? Do we weigh poor performances and breakout ones equally? They’re all valid, and they all offer their own can of worms. One tool we do have, though,  is SIERA — skill-interactive earned run average — that does a decent job of predicting a pitcher’s ERA the following year.

Because public research is both awesome and vast, especially if you believe in the ultimate collective pursuit of attaining a stronger understanding of the game, there are also studies that dispute whether SIERA or xFIP is better at predicting this. But for our purposes, we’ll stick with SIERA because it doesn’t assume a league-average home run rate as part of its foundation. MLB has pretty much proven to us that we can’t count on anything about the ball from year-to-year or game-to-game, and we know the seams have had a huge influence on how the ball carries in recent years.

Here’s the full list of guys who have thrown at least 40 innings, sorted by the biggest gaps between ERA and SIERA. In the chart below, three of the more interesting names are highlighted.

SIERA Curiosities, 2020


 Framber Valdez


It’s been a year of relative tumult for Houston and they’ve thrown nearly anyone they’ve got into their rotation. Valdez has made good on his chance by cutting more than half his free passes. That’s a big deal for any pitcher but he’s had walk rates into the double digits since 2017. The solution is a typical Astros thing, too. Check it out:


The org has been cleaning up release points for a lot of pitchers for a while, including a couple of the game’s best in Gerrit Cole and Justin Verlander. With the way high fastballs and low breakers pair up to wreak havoc on a hitter’s swing plane, which is something else Houston embraces, the tighter release points make it even tougher to discern an offering out of the hand.

Valdez is kind of a modern oddity in that his go-to heater is a two-seamer. It’s not just his primary pitch but one he tosses more than 50% of the time. On top of that, he’s maintained his curveball use and has also made a legitimate offering of his changeup by throwing it just enough (nearly 9%) to force hitters into keeping it in the back of their minds. They’re all all moving as they has before but now it’s a legit three pitch mix that’s simply finding the zone more. When Valdez broke into the major leagues, he was only getting it over the plate about 38% of the time. Now he’s up to 53%. That’s above average now, and with lefty funk coming in around 94 mph it’s been more than enough. Houston will be stronger next year but he’s showing us a lot to buy into.


Chris Paddack


Batters have barreled up Paddack’s stuff way more this season and it’s has made for some messy results. His SIERA is a full run better than his ERA because of it. That takes him from inside the top 40 by that category to outside the top 60. The profile is pretty much identical to last year’s hyped debut across the board, though. His K:BB, velo, pitch mix — they’re all the same. The BABIP is 70 points higher but it’s sitting pretty much league average now. It’s just that guys are ripping into him when they make contact.

In particular, it’s the fastball and curve that hitters are tuning up.

Chris Paddack Pitch Results

The difference in results is massive. Let’s talk about the fastball first. He’s locating it more up in the zone while getting less ride on in it. That could make the pitch look flatter and fatter to hitters, making it far more appealing to sit on. A bit of good news is it doesn’t seem to be impacting how his changeup is working. Generally, the two have such an influence on each other that one performing poorly could mean both offerings do. He’s still be able to pull the string on his primary off-speed pitch, though.

The curveball also forces us to break out the oof meter. He’s getting more drop on it but it just isn’t working, and that could be because he’s trying to use it at the top of the zone and at the bottom, but not much below it. Last year the pitch was a work in progress and being able to bury it was critical. He worked on his mechanics and delivery over the offseason but it looks like there’s still work to be done. Developing a third pitch for him has continued to be elusive this season. It might be most important to practice patience and remember that Paddack is just 24 years old, though. Pitchers aren’t coming in at peak and plateauing like hitters often do now. He’s still providing us plenty of reasons to believe. If Valdez’s SIERA is going to represent how growth is possible, Paddack’s might represent a need to realize what’s already visible.


Tyler Glasnow


Tyler Glasnow is second in all of baseball in strikeout percentage, at 37.4%. He’s top five by K-BB rate. But his walk rate is up near 10% after he lowered it each year in the majors before this one. We know the stuff can and often is overpowering, but he still shakes out as just a two pitch guy. His ERA could be getting tagged because of how those pitches act, too. His fastball finds the zone more than 60% of the time he throws it while the curve only lands there about 30%. If you know a kneebuckler’s coming that’s nearly impossible to catch with your barrel, but you also know you’ll probably get twice as many fastballs and probably get one that’s hittable, the plan of attack becomes clear.

Batters have generated a pedestrian wOBA against Glasnow’s heat but his command and pitch mix might always make for results with a wide range of outcomes, even if his SIERA suggests he could be better. As dominant as he’s been, he hasn’t been been wart-free. Get ready for another offseason of heated debates on what exactly to do with him.


The Others


Notably, Zach Eflin showed up as the pitcher with the sixth-biggest gap in baseball between his ERA and SIERA. I covered him in depth last week and he’s worth monitoring because he keeps developing his stuff. An aging Max Scherzer showed up in the results for this query. His K-BB rate is still excellent but we might have to start wondering about his health and how it impacts his results. Frankie Montas is walking a ton of guys again after last year’s breakout and that could be a big deal for him moving forward. It’s hard to argue against runs given up when you’re giving so many free passes. Kevin Gausman has taken a huge step forward with the Giants and his SIERA suggests there’s even more in the tank, which would be wild, given his career path to this point.






Tim Jackson

Tim Jackson is a writer and educator who loves pitching duels. Find him in the PL Discord, editing, managing, and podcasting with @BREAKINGPodPL here or writing at Baseball Prospectus.

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