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Why is Jhoan Duran Scuffling?

Minnesota’s fireman is suddenly fallible. Let’s meander through the data and see if we can pinpoint the issues.

Pittsburgh Pirates v Minnesota Twins Photo by David Berding/Getty Images

I’ve never analyzed Jhoan Duran before. Frankly, there hasn’t been a need for it. Most of what I write about has to do with trying to figure out why someone is succeeding or what they might need to change to succeed.

It doesn’t take a full article on Twinkie Town to explain why Jhoan Duran has been successful. He throws 102 mph with an ungodly curveball and a splitter that touches 100 and he throws all three of those pitches for strikes. There isn’t much I’m going to add to that. It’s about as self-explanatory as it gets.

Last year, as a rookie, he had a 1.86 ERA, a 2.52 FIP, struck out 33.5%, and walked just 6.0% of the batters he faced. Altogether he accumulated 4.56 win probability added (WPA), the third-most among the 347 MLB pitchers that threw at least 50 innings. He was unquestionably one of the best relievers in all of baseball.

Through June of this season, it was essentially more of that from Duran. After converting a save opportunity on July 1st in Baltimore, Duran had a 1.41 ERA, a 34.1% strikeout rate, and his 1.84 WPA was tied for 17th-most out of 414 pitchers who had thrown 20 or more innings this season. Somehow, he was also throwing harder than ever, averaging 101.9 mph with his fastball, a full tick better than the mind-boggling 100.8 mph he averaged last season.

On July 2nd, Duran came into the 8th inning of a 1-0 ballgame to face the heart of the Orioles lineup. Three hits, a walk, and two runs later he had a blown save that became a loss.

Beginning with that day in Baltimore, Duran has a 4.64 ERA, a 3.54 FIP, and -0.65 WPA across 21 appearances and 21.1 innings pitched. Of course, that’s not a large sample, and relief pitching results can often look terrible in arbitrarily chosen stretches. But, he has been scored upon in 10 of his last 21 appearances after that happened in only 7 of his first 29 appearances this season and in just 10 games total last season (57 appearances).

What’s Going On?

I’m going to put a bunch of my favorite numbers side by side and see what we can find. We’ll start with the FIP inputs, then go to the “luck” stats, and then to contact quality and plate discipline numbers:

Data from FanGraphs

I’ve highlighted in red some of the areas that jumped out to me. There does appear to be some misfortune involved, reflected by the batting average on balls in play (BABIP) and left-on-base rate (LOB%). Both of those were probably over-performing earlier this season and now have swung back very hard the opposite way during this tough stretch.

At the same time, some of that appears deserved. Duran has been easier to hit and getting hit harder. That’s evident from the contact rate, exit velocity, strikeout (K%), and swinging strike rate (Sw-Strike%) data above.

Physical Pitch Characteristics

Next, let’s do the same thing, but from a physical stuff perspective:

Data from Baseball Savant

His pitch mix, velocity, and spin rates are more or less the same. He has lost a touch of velocity on all his pitches, but it’s still the absolute top-of-the-line heat in the game today.

What stands out, though, is that he is dealing with some movement profile changes. Notably, his fastball has lost an inch of induced vertical break, something that Matthew Braun and Jeremy Maschino pointed out a couple of weeks ago.

That means it’s not resisting the effects of gravity as much as it did before, and is, therefore, less deceptive. Said differently, with less vertical movement his fastball looks slightly more like what batters would expect.

Similarly, his hybrid splitter-sinker has also lost some induced vertical movement, while his curveball has gained almost an inch.

His overall Stuff+ hasn’t changed a lot, but it has declined from 132 to 126.

Cleveland Guardians v. Minnesota Twins
Jhoan Duran has not been as dominant in the second half
Photo by David Berding/MLB Photos via Getty Images

The samples are not quite the same size – Duran threw 491 pitches in the before sample and 383 in the after. The run value figures are cumulative (and positive is good), but you can see pretty clearly that both his four-seamer and curveball have been much less effective.

Opponents have crushed Duran’s fastball since early July, despite the fact that it’s still 101-102 mph. In 35 plate appearances ending on his fastball, they’ve slashed .310/412/.655 (.446 wOBA), which is very different than the .171/.275/.257 (.247) they produced in 42 plate appearances prior.

A similar story, although not quite as pronounced, has played out with his curveball. In 37 PAs before early July, opponents hit .118/.189/.235 (.193 wOBA) against it. In 27 plate appearances since that’s been .240/.259/.400 (.278).

The Context of Duran’s Fastball

At this point, you might be, rightfully, wondering how an inch of movement lost can have such a profound effect on the results of a 102 mph fastball. The short answer is that velocity buys you a lot, but it isn’t everything.

The characteristics of Duran’s four-seam fastball, other than its super-premium velocity, are somewhat unremarkable. His spin rate is only in the 13th percentile. Its vertical movement is a little more than 10% below average for its velocity. It does have above-average horizontal movement, but that tends not to be the same kind of bat-missing movement that vertical movement is, especially up in the zone where Duran lives with his express.

All of that is reflected in the relatively pedestrian 106/108 Stuff+ grades on the pitch. Despite that 100th-percentile velocity, Duran’s fastball ranks 137th by Stuff+, among the 613 pitchers to have thrown 10+ innings this season.

Whereas four-seam wizards like Duran’s teammate, Joe Ryan, have mystifying four-seamers thanks to the other, non-velocity, characteristics of their fastballs, Duran is the opposite. His four-seamer is more of the brute force variety. Take away some of Duran’s vertical movement and his four-seamer is easier to get the bat on.

It’s In The Release

Whenever I see movement changes, I look for spin direction and release point changes. Duran’s spin directions have not changed on any of his pitches, per Alex Chamberlain’s pitch leaderboard. Neither has the approach angle on any of his offerings.

But his release points have changed. Here’s a table of his monthly horizontal and vertical release points, going back to last season as measured by Statcast:

Data from Baseball Savant

You can see that last year’s vertical release points were very consistent between 6.02 and 6.11 feet. This season, that’s been more variable between 5.96 feet and 6.18 feet, with a bit of a declining trend in August. His horizontal release has been a little more variable overall, which could just be a product of shifting his place on the pitcher’s rubber, or it could be related to the declining vertical release. Whatever the cause, the vertical release of all three of Duran’s pitch types has declined lately, while the horizontal release has moved toward third base.

You can see how those changes interplay together in this overlay of Duran’s release points this season prior to July 2 and after:

It doesn’t look like much here, but pitch movement can be affected by the tiniest of manipulations and margins. This change of an inch or more at release could be very significant to the shape of his pitches and it is certainly enough to explain the lost inch of vertical movement on his fastball.

Remember Josh Hader’s home run struggles in the middle of last season? They were largely the result of some small mechanical fluctuations in his release that changed the shape of his fastball. Duran’s changes are not as significant as Hader’s were, but they sure seem to be having an effect.

Command, Too

The release point issues could also be impacting the crispness of his command. While the aggregate numbers like zone rate and walk rate above don’t suggest Duran is having issues throwing strikes, those who have watched him pitch can tell you that he isn’t as sharp (the wild pitch that gave Cleveland the tying run on Wednesday is a good example).

To that point, the share of Duran’s pitches that are in the shadow zone (i.e., near the edges of the strike zone where they are hardest on the hitter) has decreased from 43.6% in the 1st half to 40.7%. The share that are waste pitches, way out of the strike zone, has increased from 7.7% to 9.9%. These are small samples and only a handful of pitches can change these fractions, but they are illustrative of the point.


Taken together with the over-correction of his batted ball fortune and the unforgiving terrain of high-leverage relief work, Duran is now in the position of needing to make some adjustments for the first time in his big league career.

These kinds of mechanical fluctuations happen to all pitchers for a variety of reasons. It could be nothing other than needing to make a little fix. Or it could be caused by fatigue, or an undisclosed or otherwise minor injury.

Whatever the reason behind the release point change, the Twins need Duran to get it fixed and get back to the level of consistency and dominance he’s shown before.

John is a writer for Twinkie Town and Pitcher List with an emphasis on analysis. He is a lifelong Twins fan and former college pitcher. You can follow him on Twitter @JohnFoley_21.