Starting Pitcher Last 30 Day SwStk% Gainers & Decliners — Jun 17, 2024

Pitchers change far more frequently than hitters. Their velocity fluctuates from start to start and throughout the season, their pitch mix is often adjusted, and sometimes there are games where the command just ain’t there. So it pays to review a pitcher’s recent skills, as the full season line might not tell the whole story of who that pitcher is right now. With that in mind, let’s find out which pitchers have gained and lost the most SwStk% points over the last 30 days versus the beginning of the season period.

Carlos Rodón suffered through an ugly 2023 season that saw his strikeout rate crash and ERA skyrocket to nearly 7.00. Heading into his age 31 season, he was still young enough to believe he was a serious rebound candidate. So far, the results have been mixed. While the ERA is sub-3.00, the overall skills certainly don’t back it up. His season strikeout rate remains barely above last year, while his SwStk% is almost identical. So what has happened these last 30 days?

For one, he’s gained some velocity, as his fastball has risen from around 95 MPH to just under 96 MPH. Second, he’s thrown that fastball a bit less in favor of his slider and changeup. Those changes, combined with the surge in SwStk% sound great, right? Except that his strikeout over the last 30 days has gone down! Whaaaaaat?! That doesn’t make any sense. Of course, it’s still good news that his velocity has increased, and over the last 30 days it’s averaged higher than it ever has over a full season previously. But it’s bizarre that all those swinging strikes aren’t resulting in a higher strikeout rate. Perhaps those will come to offset the low BABIP and high LOB% that will inevitably regress.

Rockies front office — “What type of pitcher would be the ideal fit pitching half his games at our hitter’s haven known as Coors Field? Well, one that allows a ton of balls in play because he doesn’t strike anyone out, of course!” That must have been the conversation that led to the team trading for Cal Quantrill, after he was coming off a 13.1% strikeout rate with the Guardians in 2023. So of course, he’s now sporting a 3.30 ERA, and once again massively overperforming both his SIERA and xERA. I’m dying to understand what Quantrill is doing that these equations are missing, as his skills are weak, yet he owns a career 3.77 ERA.

Anyway, over the last 30 days, Quantrill has thrown his splitter 7.3% more often, at the expense of several pitches, but mostly his changeup. He has also gained 0.9 MPH on his sinker, his most used fastball. So more splitters + a higher velocity sinker seems like good changes which would explain the increased SwStk%. That said, he still only sports an 18.2% strikeout rate these last 30 day, which remains well below average. The results have been there though thanks to a low BABIP and HR/FB rate, but it’s also worth noting that four of his five starts have come in away games, so he has avoided his hitter friendly home park. While this looks like a better version of himself, I still wouldn’t touch him regardless of league format. I don’t want to rely on a low strikeout guy whose getting by with better than average marks in the luck metrics, as you never know when that luck (or skills if we determine it’s truly skills he owns) runs out or deteriorates.

After a solid debut last year, Tanner Bibee has dramatically improved his skills, but a reversal of fortune has added nearly a full run to his ERA. Over the last 30 days, his SwStk% has jumped to near elite territory, driving a 32.5% strikeout rate. His pitch mix hasn’t changed all that much, throwing his slider a bit more at the expense of his four-seamer and changeup. But he’s also gained 0.8 MPH on his fastball, which now averages just above what he averaged last year. Both his slider and changeup have generated mid-teen SwStk% marks so throwing one more often compared to the other shouldn’t have much of an effect on his strikeout rate.

However, with his curveball pushing into double digits in SwStk%, all three of his non-fastballs are above 11%, while he sports a fastball that is well above the league average in SwStk% as well. The SwStk% suggests none of his non-fastballs are true standout pitches, but it’s a nice mix of good to average that gives him options if one isn’t as effective in any particular start.

Luis Gil has walked the tightrope this year, walking 12.3% of opposing batters, but posting a sub-.200 BABIP and stranding over 80% of baserunners to keep his ERA right around 2.00. I’m actually shocked to see that his SwStk% sits at just 12% and CSW at 27.8% on the season, which is well below what I expected given his 30.4% strikeout rate. Of course, he has been much better at generating whiffs over the last 30 days.

He has thrown his four-seamer and slider less often and increased usage of his changeup. It’s an odd switch as his changeup has actually been his worst pitch in SwStk%, though his slider has been below the pitch type average as well. Only his four-seamer has been above average, which is just surprising given his strikeout rate, as I certainly expected more domination from his repertoire. What’s interesting is his changeup velocity has risen by 1.7 MPH, which is pretty significant. His fastball and slider velocity have also increased, but by only 0.5 MPH. His changeup velocity has sat at 92.5 MPH, which is what many starters’ fastball velocity is at!

I’m skeptical that Gil can keep this up over the rest of the year. The walks are an issue and the mediocre CSW% suggests it’ll be difficult to maintain a 30% strikeout rate. That BABIP is due for a spike, which is going to produce a double whammy with all the free passes he gives out. He’s a sell high in my mind.

In recent years, we have seen many examples of players going to Driveline Baseball over the offseason and then dramatically improving the next season. This year seems to be a disappointing crop of graduates, however, which includes White Sox starter Chris Flexen. His skills remain similarly weak as previous years, as his ERA sits above 5.00 and ERA estimators don’t calculate he deserves that much better.

But over the last 30 days, he’s pushed his SwStk% into double digits, which shouldn’t be a big deal, except that he’s never posted a double digit mark over a full season in his career! He is thrown his fastball, slider, and changeup all a bit less, in favor of his cutter, which he has thrown 6.4 percentage points more often recently. Reducing his fastball usage definitely helps his SwStk%, as its his worst pitch at getting whiffs. However, the cutter hasn’t been any better than his slider and changeup, so it shouldn’t explain much, if any, of the increased SwStk%. On the velocity front, his pitches are mixed, with some down slightly, one up slightly, and his slider down 0.8 MPH. Overall, it doesn’t appear velocity changes has anything to do with his SwStk% surge.

So what have we learned here? Not a whole lot. He has thrown more cutters, which should increase his SwStk% a bit since he slightly cut down on his fastball usage, but he also cut some other pitches which were just as good at getting whiffs. There’s no velocity increase here. So it appears to merely be a good run. Even during this period of increased SwStk%, his strikeout rate has been just 17.4%, which is nearly identical to his full season mark. I’d continue letting him swim in your free agent pool.

After a strong spring training, Jared Jones won a spot in the Pirates’ rotation and was the talk of the town before Paul Skenes arrived. An 18.7% SwStk% over his first eight starts is impressive, but he’s regressed hard since. It’s a reminder that MLB hitters are good and it’s quite difficult to remain so dominant without hitters adjusting.

Over the last 30 days, he’s made a couple of minor adjustments to his pitch mix by throwing his fastball and curveball less often, in favor of his slider and changeup. Finally, a pitcher following what’s been most effective! His slider has been by far his best whiff pitch, so it makes sense to throw it even more, even though he’s already in the mid-to-high 30% range. His changeup has been his second best whiff pitch. On the other hand, his curve has generated a sad 6.3% SwStk%, so while he has thrown it just 5.8% of the time over the last 30 days, maybe he should just ditch it.

In terms of velocity, the only change is his changeup, which is coming in 0.6 MPH faster now. He’s still averaging 97.3 MPH with his fastball, identical to earlier in the season. Based on his pitch mix and velocity, there’s no obvious reason why his SwStk% has plummeted. Do realize his mark is still above the league average, but simply not elite like it was previously. With a strong three-pitch mix that should work against both lefties and righties, I wouldn’t be worry about the recent decline in SwStk%. I would also bet that he easily beats all his rest of season projections in both ERA (all forecasting above 4.00) and strikeout rate (the most optimistic is only 23.9%, he’s at 26.3% right now), even though his strikeout rate has been just 19.3% over the last 30 days, driving a 4.28 ERA.

Zack Littell’s SwStk% has gone from just above average to well below the league average, dropping into the single digits. On the pitch mix side, he’s mostly swapped one fastball type for another — reducing usage of his four-seamer in favor of his sinker. As you might expect, his four-seamer does generate a higher rate of swinging strikes than his sinker, so this change definitely explains some of the drop in SwStk%. Aside from that change, his velocity is down slightly across the board, but not enough to be too worried. Overall, his splitter has been fantastic at generating whiffs, but he has thrown it significantly less than his slider, which is well below average in generating whiffs. I would think he should start experimenting with throwing his splitter more and that slider less, given the vast differences in SwStk%.

With a sub-4.00 SIERA and xERA, Ryan Feltner has actually posted decent skills for a Rockies starter, but a massive BABIP and microscopic LOB% have torpedoed his ERA. It’s too bad his SwStk% has dropped into single digits recently, as you can’t afford to miss so few bats when you call Coors Field home (unless you’re Cal Quantrill, apparently).

Feltner is the first name on this list to have drastically changed his pitch mix over the last 30 days. He has upped his sinker usage by 8% and curveball usage by 9.3%, while reducing usage of his slider by 11.6% and his changeup by 5.3%. Those are big changes! Increasing sinker usage should increase GB%, but reduce SwStk% and strikeout rate, while his curveball has been his second best non-fastball in terms of SwStk%, so increased usage there should be a positive. However, reducing usage of his changeup makes no sense, as that’s been his best whiff pitch every single season of his career! This year it sports a 20.8% SwStk%, so I don’t know why he would start throwing it less. These changes right here certainly explain the drop in SwStk%, as his velocity has been fairly stable.

Gosh, I’m surprised to see Zack Wheeler’s name on this list, as he’s having another fabulous year and hasn’t allowed more than two runs during any start over the last 30 days. He has increased his four-seam usage a bit at the expense of his slider, which is a ding ding ding for suffering a drop in SwStk%. Then again, Wheeler isn’t like most, as his four-seamer is fantastic at generating whiffs. For the season, the pitch’s SwStk% sits at 13%, while his slider is only a bit better at 14.7%, so it’s no guarantee that the switch in pitch mix would result in a decline in overall SwStk%.

On the velocity front, everything is up! His fastball has gained 1.1 MPH, while everything else is up at least 0.6 MPH. That’s pretty incredible. And yet, his SwStk% is down. According to Statcast, he has reintroduced a splitter, which he had last thrown a bit of back in 2020. That has actually been his best SwStk% pitch at 20%, so perhaps he should consider throwing it even more. Bottom line is there are no red flags here, and while his ERA is unlikely to stay this low as his BABIP regresses, he should remain elite.

Yikes, Marcus Stroman has never been a big whiff generator and was sitting at just a 9% SwStk% mark earlier in the year. But over the last 30 days, he’s been at just 6.3%, which is actually second lowest among 74 starting pitchers. Of course, it hasn’t hurt him at all this season, as he dramatically overperforms both his SIERA and xERA, thanks to a career best BABIP and a LOB% over 80% for the first time.

Like Feltner, Stroman has significantly altered his pitch mix over the last 30 days. He has thrown his fastball and slider a bit less, while dramatically reducing his sinker usage. On the other hand, he has upped his splitter and curveball usage a bit, while drastically increasing his cutter usage. Yeah, he throws a lot of pitches (six, to be exact). While he throws the kitchen sink, none of them stand out. This year, his best SwStk% comes from his slider, and that sits at just 12%.

His biggest changes was cutting his sinker usage, which is a positive for his overall SwStk% considering it has generated just a 4.3% mark during the season, and upping his cutter usage, which has generated more than double the SwStk% at 10.4%. That should be a major positive for his SwStk%, so it’s odd to see his mark down over the last 30 days. Perhaps it’s it’s because his velocity is down a bit across the board, but it wouldn’t seem to be enough to justify such a lack of whiffs.

The bottom line here is that Stroman seems to be a consistently solid starter, but his skills are the weakest they have ever been in his career. With a low strikeout rate, you’re relying on the low BABIP and high LOB% to continue to keep those ratios from imploding. That doesn’t seem to be worth the risk, which makes him an ideal trade candidate if you own him.