Starting Pitcher SIERA Underperformers & Overperformers

We’re about three and a half weeks into the season, which still qualifies as a small sample size. Even though rate stats could still fluctuate wildly, especially ERA and WHIP for pitchers given their low number of innings, it’s hard for many to ignore those marks and look at the underlying skills instead as a better predictor of future results. So it’s worth reviewing a pitcher’s ERA compared to his SIERA to get an idea of whether he’s riding strong/weak skills or is being impacted more by the luck trinity of BABIP, HR/FB, and LOB%.

In addition to SIERA, I have also included the Statcast xERA metric, which accounts for opposing batted ball quality. I shy away from using that metric instead of SIERA this early because even if we might be able to say a low BABIP allowed is deserved, opposing batted ball quality is likely less stable than strikeout and walk rates, along with batted ball type profile. So it’s here to better explain what has happened so far, but I don’t think it will prove to be as predictable as SIERA.

Let’s begin with the SIERA underperformers, who might be ideal trade targets. For this exercise, I’m only going to list pitchers with SIERA marks below 4.00, so at least we know he’s shown pretty good skills. It’s not really actionable knowing a pitcher with a 6.00 ERA has underperformed his 4.80 SIERA!

Holy cow, this is quite the list of pitchers!

After failing to record more than 102.2 innings since 2019, Chris Sale surprised everyone last year by pitching 177.2 innings over 29 starts and winning the Cy Young award, all at the age of 35. This year hasn’t started the way his owners expected, thanks mostly to an absurd .422 BABIP. His xERA is nearly a full run higher than his SIERA, suggesting some of the inflated BABIP is deserved, but in 23.1 innings, that’s pretty meaningful moving forward. His velocity is fine, pitch mix hasn’t changed much, and Stuff+ a tick higher than last season to the highest it’s been since tracking in 2021. He’s a prime trade target, though at his age and given his injury history, it’s always possible he lands on the IL at some point.

I was worried enough about Aaron Nola’s velocity loss during spring training that I boldly predicted Yusei Kikuchi would outearn him this year. Unfortunately, that velocity loss has carried over to the regular season and he actually showed his worst four-seam fastball velocity during his last start. It’s therefore quite surprising that the skills remain strong and right in line with past seasons, as I would have expected a decline in strikeout rate. Normally, I’d point to the .377 BABIP, 20% HR/FB rate, and 63.7% LOB% and scream buy low, but I’m never sure what to do when those are paired with velocity losses. He’ll probably end up being fine and I’ll kick myself for thinking too hard, but then again, perhaps not.

Dylan Cease’s xERA is nearly identical to his SIERA, so that .384 BABIP looks like clear bad luck and no fault of his own. But oddly, his strikeout rate and SwStk% are both down at lows we haven’t seen since before his 2021 breakout. The velocity is fine and pitch mix similar, so there doesn’t appear to be anything to worry about. It might be tempting to worry a repeat of his 2023 is coming, but it won’t for as long as his improved control sticks. Like Sales, he looks like a great trade target.

Hmmm, the pendulum has swung the other way for Luis L. Ortiz now, huh?! Last year, he vastly overperformed both his SIERA and xFP, both by about a full run. It made it easy to plop him into the potential bust bucket this year. But wait a second, suddenly he is generating more whiffs, pushing his strikeout rate way up into the mid-20% range. But along with the increased strikeout rate has come an inflated HR/FB rate and suppressed LOB%. Both his four-seamer and slider are inducing a higher SwStk% and it might be believable given his velocity. I’m really not sure if he could or will maintain this strikeout rate, but even if he fails to, he’s got to improve upon that ERA.

Would you believe that Kyle Freeland has overperformed his SIERA over his career, despite spending his entire time with the Rockies?! His strong SIERA is due entirely to a microscopic walk rate that won’t last and a career high GB%, thanks to a hilarious 100% GB% on his knuckle curve. If I were to ever start a Rockies pitcher, it wouldn’t be one with a sub-20% strikeout rate.

Stop reading this now and buy Cole Ragans. I will still never forget how I picked him up in AL Tout Wars at the beginning of the season back in 2023 due to a spring velocity bump, just to see him stink as a reliever, drop him, then enter the rotation and dominate…on someone else’s team.

So is Taj Bradley going to be the latest example of a guy who consistently underperforms his SIERA? His SIERA hasn’t budged much since his 2023 debut, but his ERAs have been up and down, and all above 4.00. The skills here are odd, as he generated swinging strikes, but so few called strikes so he ends up with a below average CSW%, yet has still managed to maintain a mid-to-high 20% strikeout rate. That seems hard to do. Stuff+ thinks his location is the biggest problem here, which perhaps explains the inflated HR/FB rate (sounds like a future data analysis to undertake!). I’m sure he’ll record better results from here, but I’m not running to buy.

Walker Buehler improved his SIERA yesterday as I was typing this, though it was against the White Sox, so perhaps it should only partially count. Buehler’s velocity is down from past years, and while I’m guessing his SwStk% has improved after his latest start, it still likely remains in single digits, with an underwhelming CSW%. So this is clearly not vintage Buehler and unless that velocity comes back, we probably won’t see that version. I’m not very interested in buying here.

Woah, Zack Wheeler sitting with a 33.6% strikeout rate and a career best 15.3% SwStk%! A 16.1% HR/FB rate has pushed his ERA up to merely mediocre, but it doesn’t appear he’s on the verge of suffering from any sort of age-related decline.

Eduardo Rodriguez, who are you?! A 30.2% strikeout rate would easily be a career best. Unfortunately, that seems to be a major fluke, as his SwStk% is just below his career average, while his CSW% is just above, with the latter just below league average. That’s no recipe for a strikeout rate that high. Once that drops, his SIERA will rise. Perhaps he’ll prove to be a low-end shallow mixed league option, but I don’t see a breakout here with similar velocity and pitch mix as always, and nothing different anywhere else.

Now let’s move on to the overperformers.

Yikes, this list is quite underwhelming.

How on Earth has Randy Vásquez managed a 1.74 ERA while walking 14 batters in 20.2 innings, and only striking out 8? That’s a magic trick for sure! If you’re “riding the hot hand” with him in your league, even an NL-Only, stop and try trading him for anything you could get right now.

Tyler Mahle looks like a nice comeback story and we see major disagreement from SIERA and xERA here. His velocity has inched up a bit compared to last year, but still remains well down from his prime seasons. The strikeout rate rebound is nice to see, but it has come with poor control and double digit walk rate. The discrepancy mentioned at the beginning suggests that some of his microscopic .156 BABIP is deserved, even though you would never guess given his league average batted ball profile. That said, he’s obviously not going to maintain a sub-.200 BABIP or a 90.9% LOB%, and will eventually allow a home run. I would have liked to see a better velocity and Stuff+ rebound, so I’m not buying a sub-4.00 ERA.

Kodai Senga’s spring velocity decline has carried over, but it hasn’t been as bad and he’s been at 95+ MPH his last two starts. The strikeout rate has been down, mainly because of a lack of called strikes, while his Stuff+ has collapsed to below 100, thanks to declines across the board, most notably his forkball and slider. Good fortune across all three metrics has helped him here, with xERA suggesting he is deserving of some of those low rates. I would probably just hold here, unless you could swing him for someone who is clearly projected to be worth more the rest of the way.

Yuck, a 15.8% strikeout rate and 23% CSW% for Mitchell Parker, despite a double digit SwStk%. Velocity is good and pitch mix similar, while his Stuff+ is slightly higher than last year, though still well below average. I would have no interest in owning him, even in an NL-Only league.

Tyler Anderson is doing it again! He vastly overperformed his SIERA back in 2022 and then again last year, while failing to do so back in 2023. This year, his strikeout rate is at a career best, despite his lowest SwStk% since 2020 and a CSW% in line with his career. So…that strikeout rate ain’t lasting. Oh, and his control has deserted him as he has walked double digit batters. Sure, he might continue to do what he’s done to mystify the ERA estimators, but it’s a risk I’ll never be willing to take.

When Logan Allen won a rotation spot over one of my favorite sleepers this year, Triston McKenzie, I was miffed. Now Allen is sitting pretty with a 2.11 ERA and the latter was just DFA’d. Of course, Allen’s success has been accomplished with smoke and mirrors so far. His SwStk% sits at an impossible low 5.2%, so it’s shocking he hasn’t been crushed. I would want no part of him regardless of league format.

Erick Fedde lucked into a 3.30 last year in his return from KBO as a new pitcher, but at least his skills were acceptable. This year, he has walked more batters than he has struck out and generating whiffs continues to be a struggle. I’m not sure what’s going on here with his control, but since I wasn’t interested to begin with, he’s one of the easier sell candidates that might actual draw some interest.

There isn’t much different between Shota Imanaga’s SwStk% and CStr% versus last year, but his strikeout rate has plummeted. His velocity and pitch mix are similar though, and his Stuff+ is actually slightly higher right at league average, versus last year when it was below. So I’d have to imagine his strikeout rate rebounds, though that still wouldn’t justify a sub-3.00 ERA, of course. But after last year’s 2.91 mark, perhaps he could bring in a nice haul, like one of the top tier names on the underperformer list above.

It’s been quite the decline in strikeout rate for Osvaldo Bido, as his stuff has taken a hit since he got some relief innings in over the past two seasons. As an extreme fly ball pitcher in a more hitter friendly home park than he has played in, this is not the profile I want to be starting on any of my teams.

Matthew Boyd has been an oddity this year. On the one hand, his SwStk% has fallen into single digits for the first time since…2016. That’s not good. On the other hand, his four-seam velocity sits at a career high of 93 MPH, higher than his previous peak of 92.6 MPH. That seems significant, especially for a 34-year-old veteran! So it’s weird that the added velocity has done nothing for his ability go induce whiffs, while his Stuff+ is right at his career average and his four-seam’s Stuff+ itself is actually below his career average. I don’t expect this luck to continue, of course, but I’m curious to see if the increased velocity eventually leads to a higher strikeout rate, or at least what he’s posted the last couple of years.