Starting Pitcher SIERA Underperformers — May 5, 2021

Just like we are usually better off using xwOBA over a small sample to evaluate a hitter’s performance, the same concept applies to starting pitchers and using SIERA instead of ERA. So much could happen outside a pitcher’s control, such as balls finding holes through the infield or routinely finding fielders, strong or weak bullpen support stranding baserunners or allowing them to score, etc, that ERA just isn’t a very accurate measure of performance this early. So let’s dive into the qualified starting pitchers who have most underperformed their SIERA marks. Like I cautioned with xwOBA, SIERA is not meant to be predictive, so don’t assume these pitchers will all post ERAs near their SIERA marks the rest of the season. Instead, I use it by simply substituting ERA with SIERA to determine how a pitcher has pitched so far. ERA is completely meaningless to me at this point, as SIERA does a much better job summarizing the skills I care about into an ERA-like metric.

Luis Castillo’s fastball velocity was down in his first start, but jumped back above 96 MPH in his next five starts, but hopping over 97 MPH for the first time this season. So it appears we no longer have to worry about his velocity, but that’s assuming he’s back to over 97 MPH for good. Last season, he was only under 97 MPH twice all season and never below 96, so this is important to monitor. All that said, he has been all kinds of unlucky with inflated marks in BABIP and HR/FB, and a low LOB%. However, that strikeout rate has collapsed, so even with neutral luck, this isn’t the Castillo his owners thought they were rostering. All his pitches have lost some SwStk%, so you have to wonder what’s going on. Since the velocity was the best it’s been all season his last game, I’m not so sure injury is the culprit anymore, so it’s anyone’s guess what’s going on here.

It’s the same old, same old for Frankie Montas again, as he’s suffering from issues in all three luck metrics for the second straight season. Oddly, his SwStk% is the highest its been since his 2015 debut, but his strikeout rate is well down. His velocity is fine, so I would hesitatingly suggest buying here, but I know it would take balls to do so.

David Peterson’s problem hasn’t been BABIP, but a ridiculous HR/FB rate, which is also pulling down his LOB%. His skills look fantastic though, but his velocity has been inconsistent from start to start, which makes it difficult to time his good and bad starts. With a strong ground ball rate foundation to begin, I’m buying him everywhere.

Madison Bumgarner is back! You’d have no idea just looking at his ERA, but his skills have rebounded, at least off last year’s awful season. His velocity is also back over 90 MPH, which is pretty important. Batters are still hitting way too many line drives off him, but that kind of stuff is usually small sample magic that will eventually regress toward the league average. I’m not sure how comfortable I would be starting him in a shallow mixed league, but certainly in an NL-Only or deep mixed league, his owner might be on his last hair.

Charlie Morton has been as good as always and the most important thing is his velocity is back up from last season’s decline. He makes for a pretty obvious rebound.

Lucas Giolito has been as normal as ever, but the long ball has bitten him, bringing down his LOB%. That shouldn’t continue at this pace, so he’ll resemble the Giolito owners thought they were rostering soon enough.

Kenta Maeda’s strikeout rate has tumbled, but his SIERA is still just above his career average, as a ridiculous BABIP and HR/FB rate has raised his ERA. His fastball velocity is down slightly, but not enough to set off alarm bells. Given his age, I think a rebound here is slightly less likely than some of the other names on this list.

Boy oh boy, who would have ever guessed that Adam Wainwright deserved better than a 4.72 ERA?! He’s been posting SIERA marks around that number since 2017, but suddenly his skills have surged and now SIERA thinks he’s become a good pitcher again. It’s hard to believe that at age 39, he’s going to post a career best strikeout rate, so while he is likely to improve upon his current 4.72 ERA, I doubt it drops anywhere near his SIERA over the rest of the way.

Over his first three starts, Steven Matz likely got picked up in many leagues, just in time for a three game bad stretch. Overall though, his skills remain pretty good and better than they have in many years. What’s important to consider here though his that his career HR/FB rate sits above 17%, but the sample size isn’t terribly large. However, it’s very possible that for whatever reason, he’s always to homer off of so we shouldn’t necessarily expect his ERA to decline toward his SIERA. Still, over his career, his SIERA-ERA gap is much smaller and his sinker velocity is the highest it’s been since his 2015 debut. He’s probably been dropped in many leagues, especially after his last two starts, but if you have held on, continue to do so.