Jhoan Duran’s Fastball Shape Is a Moving Target. Is That a Problem? - Caretaker Exclusive

[Davy Andrews]

The flame-throwing closer saw his release point — and his velocity — drop in 2024. How did that happen, and might be be able to raise them again?

Image courtesy of © Jesse Johnson-Imagn Images

Last week, Matthew Trueblood wrote about the importance of fastball shape, highlighting the particular attributes that the Twins prize most highly. Today, I’d like to look into the shape of the team’s most exciting fastball: Jhoan Durán’s four-seamer. First, let’s address the elephant in the room: Duran saw his ERA rise from 2.45 in 2023 to 3.64 in 2024. That’s not great, but if you’re reading this site, you probably know already that Duran dealt with some really bad luck.

His FIP and xFIP were actually lower than in 2023. His .321 BABIP was higher than 85% of all pitchers (minimum 50 innings pitched). When batters put the ball in play, the 53-point difference between his wOBA and xwOBA was higher than 96% of all pitchers (minimum 100 batted balls). Results can be fluky--especially for relief pitchers, who have smaller sample sizes. I’d like to focus instead on process, because even if the results were influenced by luck, Durán’s fastball really did change shape this season. Let’s start with some cold, hard numbers, courtesy of Statcast’s new arm angle metrics.

 

As you can see, the angle of Duran’s weird, black arm has fallen five degrees from last season. His vertical release point has fallen from 6.09 feet to 5.96 feet, a difference of 1.56 inches. To be clear, things aren't quite as simple as the graphic above makes them appear. Over the past two seasons, his release point has tended to fall throughout the year.

Still, generally speaking, when a pitcher lowers their arm angle, they should expect less vertical break, more horizontal break, and less velocity. That’s exactly what happened to Duran’s four-seamer.

 

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[mluebker]

So what can be done to correct that? Is the inch-and-a-half difference something a pitcher actually can feel? And what causes it? Fatigue? Age? Changes in muscles as a result of throwing so hard and so often? It's amazing the things that can be seen and evaluated with the technology available these days, things that probably would have gone unseen in years past and dismissed with, "He's losing his stuff."

[John Foley]

The fastball misses being more variable, and the more frequent glove-side targeting, probably had some knock-on effects on his secondaries, which were also less effective last season (at least in terms of run value). They also drew less chase and whiff out of the zone than before.

If he's spraying the fastball, it's probably not going to tunnel as well with his curveball and splitter, making all of them a bit easier to discern from each other. 

Edited October 18, 2024 by John Foley

[LambchoP]

Maybe the early season oblique injury affected his performance this year. Even with his "decreased velo" this year, he's still throwing 100 mph and his curve is pretty wicked when he can locate it. He'll be just fine next year. We just better not trade him or Jax...