Starting Pitcher SIERA Underperformers — May 5, 2021, A Review

Today, I’ll review my favorite in-season ERA estimator, SIERA. This was the list of SIERA underperformers through May 3. The idea here was that absent a significant change in underlying skills (K%, BB%, batted ball profile), these pitchers should post much improved ERA marks the rest of the way as their luck metrics (BABIP, HR/FB, LOB%) normalize. Let’s find out if that did indeed happen.

Out of the 11 pitchers, 10 of them improved their ERA marks the rest of the season. Nine of the improvers did so by at least 1.00 run, while four of them improved by at least 2.00 runs. That’s some serious improvement! Even better, this group actually posted a slightly better ERA over the rest of the season than their aggregate SIERA through May 3. While the group improved in all three luck metrics, the biggest change was in HR/FB rate which was almost halved over the rest of the season. Over a small sample, the denominator of HR/FB rate could be pretty small and so the metric is therefore prone to wild fluctuations.

Luis Castillo opened the season in baffling fashion with down velocity and an ERA over 6.00. That’s not what fantasy owners paid for! He completely turned his season around the rest of the way though, as all his luck metrics rebounded and he gave fantasy owners exactly what they paid for after that bumpy first month. What’s interesting is even that early SIERA was over 4.00, which was a disappointment, so it was a pleasant surprise that he also got his ERA well below his disappointing early SIERA.

After posting a 5.60 ERA in 2020, it would have been easy to write off Frankie Montas, but if you did, you missed out on truly awesome performance the rest of the way. All his luck metrics improved immensely, and he ended up posting a career best strikeout rate and the second lowest walk rate of his career. His skills have been up and down though (just look at those seasonal SIERA marks), so it’s anyone’s guess what you’ll get in 2022.

David Peterson was the only pitcher on this list who got worse, posting an ERA more than a full run higher than that early mark! His skills definitely declined over the rest of the season, but overall they remained decent enough to be worth a look in deeper mixed or NL-Only leagues next year, depending on his health. He’s not going to allow another 22.4% HR/FB rate again!

Charlie Morton looked like an obvious buy target and he ended up posting an ERA just below 3.00 the rest of the way. His early season 5.00+ ERA was the result of a low LOB% and high HR/FB rate, both of which improved over the rest of the season, while his BABIP fell to a career low. So sure, the BABIP was lucky, but on the season, he only marginally outperformed his SIERA, as his skills remained strong. Still, at age 38, you have to wonder how much he has left.

Lucas Giolito’s LOB% skyrocketed from just 66.5% early to just over 80% over the rest of the season. That, combined with his HR/FB rate almost being halved, resulted in normal results the rest of the year after a disappointing first month. His strikeout rate did slip below 30% for the year and it never exceeded 28% from Jun-Sep after the sticky stuff ban, so he might be a bit riskier next year if he can’t figure out how to compensate.

Kenta Maeda did improve, but not to the degree his owners had expected. Turns out, he wasn’t healthy and his season ended up being cut short by TJ surgery. At his age, he’s now a complete wild card when and if he returns.

Merrill Kelly isn’t exactly the exciting buy low candidate we all strive to acquire, but he was perfectly acceptable in deeper leagues the rest of the season as his BABIP and LOB% normalized. The strikeout rate drop below 20% really cut into his value though and he’ll therefore remain an afterthought in the majority of leagues as even deep leaguers chase upside.

Can you believe that Adam Wainwright opened the season with a 4.72 ERA?! He went on to post his lowest ERA since 2014 as his BABIP fell to the lowest mark of his career over a full season. Given his massive SIERA outperformance and age (40), he’s one of the most obvious bust candidates in 2022, though that depends on whether your leaguemates focus more on ERA or SIERA and the underlying metrics.

After a hilarious 9.68 ERA in 2020, did anyone really want to touch Steven Matz as he opened the season with a 4.78 ERA? He actually made himself into a shallow league asset the rest of the season and now in the National League in a pitcher friendly park, has a chance to match his 2021 performance.