Edwin Diaz searches for his slider

New themes emerge each postseason, and through two rounds of play the 2024 playoffs have rendered exceptional relievers not only mortal, but uncharacteristically vulnerable. Devin Williams, Emmanuel Clase, Josh Hader, and the Phillies triumvirate of All-Stars have all wobbled this October; three of them have effectively sent their teams home. 

Which leads us to Edwin Diaz. 

Diaz missed all of last year with a torn patellar tendon, and the Mets eased their All-Star closer back into action. But as New York scratched and clawed its way toward an improbable playoff bid, they unleashed Diaz in ways they haven’t before. As September waned, manager Carlos Mendoza simply reasoned, “it’s big boy time.” Diaz was onboard. He threw 103 pitches in an eight-day stretch spanning the final weekend of the regular season through Game 2 of the NLDS.

At that point, it seemed fair to wonder whether Diaz’s workload had caught up with him. In Game 2, the Mets tasked Diaz with preserving a skinny one-run lead against the heart of the Phillies order. Philadelphia scored three runs, spurring an eventual 7-6 victory. 

“His slider is a little bit more arm-side right now than we would like it to be,” Mets pitching coach Jeremy Hefner told The Athletic. “The (velocity) is there. He’s still getting ahead of hitters at a pretty good clip. We’ve just got to get the slider to the glove side more often.” 

Diaz threw 12 sliders in Game 2, and only one of them had more than one inch of glove side movement. It’s probably not a coincidence that Kyle Schwarber (more on him soon) swung and missed on that pitch. 

Diaz is at his best when his slider is sharpest. But in 2024, after a year on the sidelines, Diaz’s slider lacked the same lethal qualities that spurred his domineering 2022 season. 

	Stuff+	Location+	Usage	Run Value	xwOBA
2020	132	93	38%	2	.215
2021	145	98	38%	10	.175
2022	165	102	58%	22	.175
2024	133	98	48%	2	.223

By a number of different metrics, Diaz’s slider — while still good — is not what it once was. The characteristics of the pitch are worse, and both the actual and expected outcomes have taken a step back, too. Diaz’s slider is most similar to the 2020 version of the pitch. It’s very good, but not otherworldly.

Part of that may be because it’s inadvertently rising. In May, Ben Clemens explored this phenomenon for FanGraphs, noting that for Diaz and his unique gyro slider, “getting the ball to fall more is key.” 

“You want the path to diverge as much as possible from normal fastball shape,” Clemens wrote. “Instead, his slider is hanging up in the zone.”

This year, Diaz’s slider fell 2.5 inches less than similar-looking sliders, per Baseball Savant. In 2022, it fell 0.7 inches less. That creates a disconcerting tendency for the slider to hover in the middle of the plate. 

What does that look like? Well, here’s a sharp Diaz slider from April 2022, which Schwarber swings over. It has an Induced Vertical Break (IVB) of 3, close to the center of the break chart. 

And here’s a slider that Diaz threw Schwarber in May 2024, one that was fouled off. It has an IVB of 6. Whereas the bottom dropped out of the previous slider, this one flutters. 

In August, Diaz surrendered a pair of back-breaking home runs to potent left-handed hitters — a go-ahead, eighth-inning grand slam by Corbin Caroll and a walk-off blast by Jackson Merrill — off his slider. The one he threw to Merrill, especially, had poor shape: An IVB of 9 and an inch of arm side run. If it looks like it hangs in the middle of the zone screaming “hit me,” well, it practically did. 

Since then, Diaz changed his attack plan. In September, he threw his slider just 24.2% of the time to left-handed hitters, his lowest single-month slider usage against LHB since 2019. 

He even altered his approach against hitters he’s dominated. Take Schwarber, who entered September 0-for-6 with four strikeouts against Diaz. In September, across two at-bats, Schwarber saw 15 pitches from Diaz. Only three were sliders. 

Which leads us to Game 2, where Diaz faced Schwarber, Bryce Harper, and Bryson Stott. Unexpectedly, he went back to his slider, throwing five to Schwarber — and escaping thanks to a wild check swing — and seven combined to Harper and Stott. Of the four consecutive sliders to Stott, all had just 1 inch of glove side movement. The fateful one, ending in a go-ahead, two-run double, caught too much plate. 

In Game 4, Mendoza called on Diaz — aided by two-days of rest — to slam the door on the Phillies and vault the Mets to the NLCS. Quickly, things grew precarious. 

After walking JT Realmuto on five pitches, Diaz threw five consecutive fastballs to Stott, who earned a walk. That coaxed pitching coach Jeremy Hefner to the mound. During the meeting, the Mets instructed Diaz to throw his fastball in the zone — or, more or less, right down the middle.

He obliged. Kody Clemens, another left-handed bat, received four fastballs and a slider. The slider went to the backstop. Clemens went down swinging on a fastball. Brandon Marsh — yep, another lefty — saw four fastballs and popped the last one up. Two down. 

And so up stepped Schwarber, 0-for-9 with seven strikeouts against Diaz in his career. Since their first head-to-head meeting in 2021, he had seen 45 pitches from Diaz, two-thirds of them fastballs. At this point in the game, Diaz appeared to have morphed himself into a one-pitch pitcher. He had not yet landed a good slider, but also didn’t seem to mind. Hanging one to Schwarber could be catastrophic. 

Schwarber was most certainly aware of gestures all this. 

Naturally, Diaz uncorked three straight sliders, the first of which had three inches of glove side movement — the most of any slider he threw in the NLDS. It caught a lot of plate, but it was lower in the zone, and a smidge further outside than the helicopter he threw Stott. That made the difference. And it certainly didn’t look like Schwarber was expecting it, and who could blame him? Against left-handed batters, from Aug. 1 on, only 15% of Diaz’s 0-0 pitches were sliders. 

Diaz’s fastball will draw the headlines — it’s how he rescued himself from the inning, and he did unleash a 101 mph fastball to fan Schwarber and induce a mob scene at Citi Field. It was the fastest pitch Diaz has thrown since 2022. 

But the slider is more important. By the time the Mets begin Game 1 of the NLCS, Diaz will have thrown just 23 pitches across the last six days. It may as well be a lifetime’s worth of rest. And it gives the Mets an opportunity to get his slider right. New York’s bullpen is mercurial, strengthened in recent days by Ryne Stanek and David Peterson, weakened by Phil Maton and Jose Butto. Ultimately, so much of the stable’s success relies on Diaz’s ability to be a stopper at the backend. Few of the game’s elite have performed this postseason. Many are home because of it. Diaz has a chance to continue to rewrite his narrative. And it starts and ends with chiseling his slider.