Edwin Díaz’s Fastball Is Broken-er

Díaz's fastball might be broken, but there's still hope.

After a messy 2019, I have been perhaps Edwin Díaz’s biggest apologist. Sure, the 5.59 ERA is ghastly, and the home runs are concerning, but aren’t home runs the noisest statistic of all? I mean, let’s not forget, 2019 was one of the most home run-friendly years ever, so maybe we shouldn’t overreact — especially because his wOBAcon is so much worse than his xwOBAcon. Well, I’ve thought it through — and there’s merit to this line of thinking — but underperforming and regression are not mutually exclusive. And Díaz has legitimately regressed.


Lost Delivery


Before I start to sound like a downer on Díaz, I think the juiced ball is at least in part to blame for his down year. There were many pitchers who lost pitches in 2019. Masahiro Tanaka lost his splitter. Noah Syndergaard lost his slider. A lot of pitchers lost feel for their pitches! So perhaps we shouldn’t be surprised that Díaz appeared to lose the feel for his slider.

But also, it goes beyond just losing feel for a pitch. Díaz has seemingly lost the feel for his delivery as a whole. Consider his dropping arm slot:

Now, this has been discussed before. There was a community article over at FanGraphs discussing this very thing. Since Díaz’s breakout 2018 season, he’s dropped his arm slot by about 4.8 inches on average. That may or not seem significant, but I think it’s wreaking havoc on his fastball. Some pitchers are able to throw out of a low arm slot and still get elite active spin and ride on their fastballs (see: Josh Hader). But for the most part, this is a difficult thing to do.

Let’s take a look at Díaz’s vertical movement on his fastball:


It’s perhaps not as obvious as his dropping release point, but the ride that Díaz used to get on his fastball has been dropping over the past two years. To make it easier on you visually, I added a red line to show that, compared to the eight or nine inches of ride he used to get, he’s only getting a touch above seven now. It appears that the relationship between Díaz’s release point and fastball ride are correlated, which shouldn’t be a surprise. As he’s dropped his release point, he’s converted the ride of his fastball to more horizontal movement.


Relieved of Command


So, less ride and more run. But it’s not only his pitches themselves. He seems to be off mechanically too (and the two are probably related!). All of this is probably going to make his fastball more difficult to command. It’s not only a matter of pitch quality — Díaz’s pitches have been deteriorating — but I think this is affecting where he’s putting his pitches now too. Before, he could get away with not commanding the ball super well. When you’re pumping in a 98 mph fastball with good ride and a plus slider, you’re afforded more leeway than, I don’t know, Kyle Gibson. But now, he doesn’t have that luxury. And we know location matters.

Here’s where Díaz located his fastball in 2018, his breakout year:

In 2019:

And then this year:

His fastball command has completely unraveled. The thing is, the more tail it gets, the more difficult it gets to command it. Per Baseball Savant, he’s gone from a little less than 11 inches of run 2018 to 12.4 inches in 2019 and now 12.5 in 2020. (Note: It was 13.0 a few days ago.) It’s getting so much superfluous arm-side movement now that it’s being mislabeled as a sinker about one-fifth of the time. This could be a Hawk-Eye thing, but if you look at Baseball Savant, it will tell you that Díaz threw a sinker less than 1% of the time in 2018 and 2019. Now? It’s claiming he’s throwing one more than 10% of the time.

A timely tweet from Connor Kurcon the other day:

Much has been made of Dustin May’s sinker recently. The thing is, something about that added movement isn’t conducive to limiting hard contact. It could be lessened command of the pitch, or it could mean that that extra run isn’t being converted into ride. (It’s probably both!) Whatever the reason, more tail doesn’t necessarily mean better for high-velocity fastballs. In fact, it seems like it means it’s worse for them.

So there’s that. I think Díaz has a worse fastball, and it’s coincided with worse command. He also hasn’t thrown his slider to where it plays best, which is below the zone. But also, part of Díaz’s allure is deception. He’s got a lot of funk and moving parts in his delivery, and that makes for a lot of distractions for hitters. Add in that he can pump in 100 mph fastballs and a good slider and it makes for quite the uncomfortable at-bat. Of course, Díaz had a quite troublesome 2019, so it’s hard to say that hitters are all that uncomfortable nowadays.

Take a look at a delivery from 2018:


And then from the other day:


The thing about Díaz is, yes, he can touch 100 mph, and he throws a sick slider. But also, he’s got a really whippy arm action, and he’s got levers flying all over the place. That makes it hard on the hitter when there’s so much going on. One of these things that make for deception is what I’ll describe as a glove flash that Díaz does, where he coils his glove arm and flips his wrist over as he delivers the pitch.

Focus on his glove. Here it is in 2018:


And then this year:


The glove flash is one thing. I’m sure it’s distracting for the hitter, and so he theoretically has lost some deception, but it goes deeper than that. On the top, you can see how much tension there is in his glove arm, keeping his wrist torqued, flipped up completely. This is all helping him keep his front shoulder closed. On the bottom, his glove arm has much less tension, which is probably why his front shoulder is flying open more than in 2018. This, theoretically, causes a domino effect throughout the rest of his delivery.


Safe on the Slide


In 2018, I wrote about how Díaz was throwing his slider more, and then two months later, I wrote about how his fastball and slider tunneled well together, which helped his fastball play up.

Last year, Díaz seemed to struggle with the feel for his slider — it’s a big reason why his slider xwOBA jumped from .165 in 2018 to .279 in 2019. Tim Britton wrote that he tweaked his slider grip to mirror Jacob deGrom’s last September, and now it seems like he’s got it back for good. To me, that’s the key. I’ve been pounding the table for Díaz to throw his slider more since he was with the Mariners, and he finally appears to be doing that.

Díaz’s monthly pitch usage, since 2018:

In July, Díaz threw his slider more than he has since June of 2019, and then so far in August, he’s thrown his slider more than he has since May of 2018. The thing about his slider is that it’s a far better pitch than his fastball. Perhaps not in a vacuum, but no pitch is! By swinging-strike percentage, his slider’s career 27.2 easily bests his fastball’s 13.2. By pVAL, his slider’s 23.6 (and 1.6 pVAL/C) is, again, far greater than his fastball’s 14.9 (and 0.5 pVAL/C).

Now that he’s got his slider back, Díaz ought to lean on it. He should have been doing this all along, but for the foreseeable future, he’s got a declining fastball. Since 2019, his issue has been that he hasn’t been able to command his fastball, so he’s thrown it out of the zone more. Even when it is in the zone, his fastball has been progressively getting hit harder since 2018. That continues to be an issue, but it’s one that can be mitigated by throwing his slider more.

And so, the fastball is broken. That continues to be true. In 2019, the issue was that he’d lost his slider and his fastball command. As I see it, the fastball command won’t be back this year. But his slider? It seems like it’s back. His fastball figures to be the bugaboo for now. If he continues to throw his slider as much as he is, he may be able to stave off some poor outings and hopefully quiet the insufferable Mets fans that have been vilifying him for nearly two years now.

Feature Graphic Designed by James Peterson (Follow @jhp_design714 on Instagram & Twitter)

Michael Ajeto

Michael writes about the Mariners at Lookout Landing, as well as here at Pitcher List. You can follow Michael on Twitter @dysthymikey, or you can not.

2 responses to “Edwin Díaz’s Fastball Is Broken-er”

  1. Josiah DeBoer says:

    So. Good.

    Excited to see if he leans on the slider, as its one of the most fun pitches in baseball to watch.

    • Michael Ajeto says:

      Thanks man!

      I’ll be watching closely as well. It’s been sad for me to see him struggle after being so overpowering with the Mariners. Fingers crossed!

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