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Justin Dunn could use a tweak or three

And more likely three.

MLB: Game Two-Oakland Athletics at Seattle Mariners Darren Yamashita-USA TODAY Sports

Last week, I wrote about the Mariners’ acquisition of Chris Flexen. As it stands, Roster Resource has it that the Flexen signing will bounce Ljay Newsome from the sixth spot in the rotation. While Newsome has his fair share of weaknesses, Dunn finished second-last of all starters with 40 or more innings with a 3.5 K-BB%. And so, if you ask me, I think Dunn should have been the pitcher to receive the fade from the rotation.

Heading into 2020, I was bummed about Dunn’s performance in his 2019 cup of coffee, but I chalked it up to nerves. He looked visibly nervous during his outings, and so I figured the nerves would subside after a full offseason and four big-league outings under his belt. A reasonable enough thought.

That didn’t happen! Dunn posted a 4.34 ERA and 6.54 FIP, 3.5 K-BB%, and 1.97 HR/9 in 2020. He looked incredibly shaky in terms of command, and seldom overwhelmed hitters, given that his repertoire currently leaves a lot to be desired.

For a while, I remained relatively optimistic about Dunn. I considered him a starter when he arrived from New York, and I considered him a starter when the 2020 season began. Now? I’ve soured pretty considerably, and that’s because the more I look into Dunn, the more skeptical I become that he’s a big-league starting pitcher.

The bulk of my thinking is that there isn’t any facet of his game that’s overwhelming. He doesn’t have big velocity, he doesn’t spot the ball especially well, and I would hesitate to describe any of his offerings as plus. And so, that’s where my analysis is going to go! I really, really don’t like his repertoire.

Here’s a fastball to Cody Bellinger:

A strikeout! Against Bellinger, no less. By its pitch properties, I like his fastball just fine. It doesn't get much zip, it sits at 91 mph, but he gets solid raw and active spin on it. When it’s at its best, it has plenty of ride, but it lost some this year as he lost a very precious tick of velocity on his fastball.

But his fastball’s not always at its best! Here’s a fastball against Robbie Grossman:

Dunn’s 28.0% CSW ranked in the 34th percentile of starters in 2020, sandwiched between Nick Margevicius and Yusei Kikuchi. That means that, in terms of converting fastballs to called strike or whiffs, Dunn was in the bottom-third of starters. That’s a problem! When you don’t do a good job of throwing your fastball your strikes, you have to make it up with your other offerings. Given that he throws his fastball over half of the time, he has a lot of ground to make him up with his secondaries.

Let’s take a look at his pitches. First, by pitch velocity and horizontal movement:

Here, I can see a few issues present in his pitch ecosystem. Perhaps most prominently, Dunn’s slider and curveball are pretty similar pitches. While he judiciously uses his slider as his out pitch, he uses his curveball frequently as a get-me-over pitch.

Here’s an overlay of his slider and curveball, courtesy of Pitcher List’s Alex Fast:

This isn’t the best angle, but you can see that the two don’t differ very much. The slider is a little harder, while the curveball is more sweepy. They’re separated by just 4 mph! In my opinion, these need to be turned into two distinctly different pitches.

My suggestion? Get rid of the horizontal movement and transfer all of it into drop.

Here’s Dunn’s curveball:

Pretty slurvey, very little depth. It’s a really unexceptional pitch, if you ask me. He should change that! One way would be to model his after another pitcher’s, and there are a few pitchers that have curveballs he could try and mold his into.

My proposal? Luke Weaver’s:

Given Dunn’s slider profile, he needs a curveball with a lot of separation, whether that’s by a large velocity differential or vertical drop. (Or perhaps both!) Weaver’s curveball would likely get him there by both accounts. So that’s the first tweak: separate the curveball and slider!

Then there’s his changeup! His changeup is not good, as it stands.

Here’s an overlay of his fastball and changeup, once again, via Alex Fast:

It should be pretty apparent that this isn’t the most ideal camera angle or pitch pairing. Dunn doesn’t go to his changeup much, which is probably because he knows it’s not a strong offering. It gets little to no separation from his fastball, which is the most crucial trait of a changeup. Dunn’s doesn’t separate vertically, horizontally, or by velocity. Here’s a graphic to illustrate just how poor of a pitch Dunn’s changeup currently is:

Changeup shown in green

See the orange? That’s showing sinkers by league-average movement. Notice that his changeup (in green) is nearly identical to it. That means his changeup is pretty much a sinker by movement! That doesn’t bode well, given that the average sinker is thrown at 91 mph, while his changeup sits at 87 mph. In other words, his changeup is essentially a really slow sinker! I’ve seen many people suggest that they think his changeup will eventually become a workable offering. I’m not convinced that that’s true, and if it’s not, it might be time to look into throwing a splitter, or perhaps trying that grip Trevor Hoffman showed him.

If I’m the Mariners, I’m not sure I would find it particularly challenging to help Dunn make some adjustments. After all, they’re one of the more progressive teams in baseball as it pertains to player development and pitching. If Dunn goes into 2021 with the same repertoire — and I have a bad feeling that is what will happen — then I will consider it a considerable mistake. Maybe he’s not open to the organization meddling with his pitches, but I find that hard to believe.

It’s funny. This time around, the more I looked into Dunn, the more I could see myself buying in on him with just a few tweaks. I said before, he’s not overwhelming by any means, but he has the tools to put a solid package together. My suspicion is that he will inevitably fail to do so, and I will consider that a failure on the Mariners’ player development. He’s still the same pitcher that made us think he could be a mid-rotation starter. The odds of that seem to be getting slimmer by the day, and we might end up settling for a strong two-pitch reliever in the backend of the bullpen.