Former Mets General Manager Brodie Van Wagenen made a highly controversial deal four years ago, acquiring Edwin Díaz and Robinson Canó from Seattle for a package headlined by top prospect Jarred Kelenic. Canó provided ample name recognition, but Díaz was who was truly coveted, having posted a 1.96 ERA (1.61 FIP, 1.78 xFIP) over 73 ⅓ IP while mowing down 124 (44.3 K%) and saving a Mariners franchise-record 57 games during 2018.
However, after firmly establishing himself and being adequately acknowledged for his exceptional performance a year prior, Díaz crumbled. During his first season in Flushing, Díaz posted a wildly uncharacteristic 5.59 ERA over 58 IP. He simply wasn’t impactful – his Brl/BBE% (10.1%) and Hard Hit% (45.7%) increased by 6.8% and 10.4% from a year prior, placing him in the eighth and second percentiles, respectively.
Considering his 2019 batted ball profile, it’s far from a surprise Díaz’s performance was inadequate. As Alex Chamberlain deduced, the relationship between barrels per batted ball event (Brl/BBE%) and expected weighted on-base average (xwOBA) showed a Pearson correlation coefficient of 0.93 for 2019 hitters.
Díaz seemingly couldn’t keep the ball in the park, conceding 15 HR during 2019. His 2.33 HR/9 was the worst among qualifying RP, and his 26.8% Home Run to Fly Ball rate (HR/FB%) only bested Jared Hughes (28.9%) and Joe Biagini (27.5%). 
Each poor underlying metric from Díaz’s 2019 contributed toward those who faced him slashing .258/.332/.502, while he accumulated 7 Blown Saves. The 7 BS aren’t even indicative of how much Díaz struggled to shut the door in his role as New York’s closer.
42 ⅓ of Edwin Díaz’s 58 IP during 2019 came during the ninth inning, where he posted a 7.23 ERA. And using a preferable save style metric for evaluating a reliever’s influence, Díaz’s 2019 would continue being depicted even worse than his 7 BS.
A Shutdown (SD) or Meltdown (MD) is determined by a relief pitcher’s WPA (Win Probability Added), creating a direct and impactful way of evaluating a relief pitcher’s performance. During 2019, Díaz was credited 12 MD, meaning his WPA was -0.06 or worse during 12 separate outings.
Díaz’s 2019 WPA was third worst among qualified RP (-1.75), eclipsing only Adam Conley (-1.80) and his former teammate, Juerys Familia (-1.77). Furthermore, using Leverage Index (LI) for contextualizing Díaz’s WPA, Díaz’s 2019 WPA/LI (-1.11) again eclipsed only two other qualified RP – Conley (-1.14) and Conley’s teammate, Wei-Yin Chen (-1.18).
Since December 2018, when Díaz was acquired, a lot has changed.
Van Wagenen was fired, Canó was suspended and DFA’d, and Kelenic has slashed .168/.251/.388 while a Mariner. And since Díaz’s disaster of a 2019 campaign, he has rebounded extremely admirable.
While Díaz pitched admirably in each season since his disastrous 2019, he totaled only 25 IP during a pandemic shortened 2020 season, and his 3.45 ERA (3.47 xFIP) and 34.6% K% during 2021 were far from what was expected of him when he was acquired. But a once highly controversial trade transcended from a potential disaster into a quite undeniably impactful acquisition when Díaz rediscovered his 2018 dominance, completely redeeming himself during a campaign that equaled or exceeded what any other relief pitcher has produced in recent memory.
Over 62 IP, Díaz produced 3.0 WAR by way of a 1.31 ERA (1.69 xERA, 0.90 FIP, 1.04 xFIP, 1.11 SIERA) while compiling 118 SO (50.2 K%). Each aforementioned metric led among every qualified relief pitcher, and by a considerably large and unprecedented margin, too. His FIP led by .93 (Andres Muñoz, 1.83), his xFIP by .97 (Chris Martin, 2.04) and his SIERA by .63 (Muñoz, 1.74).
A very much absurd campaign made his 2019 inadequacy feel unimaginable, and furthermore made his extraordinary 2018 seem ordinary. Díaz’s dominance was acknowledged and quickly honored when he signed a record deal for a relief pitcher with New York before free agency began, ensuring he would continue closing in Queens for the foreseeable future. 
Diving into Edwin Díaz’s dominance during 2022, it’s understandable why he was deemed worthy of a record deal. Already established was Díaz’s unmatched xERA, FIP, xFIP, and SIERA, but examining every other category where Díaz was unrivaled by identifying each integral metric for determining a pitcher’s performance can further characterize his historic campaign.
What made Díaz’s campaign beyond praiseworthy was how often he overwhelmed and overpowered whoever he faced during 2022. By mowing down 118, Díaz K’d 22 more than any other relief pitcher (Devin Williams, 96), and his K% (50.2%) was 10.2% above another relief pitcher (Williams’ 40.0%).
Since 2015 and among every qualified pitcher (minimum 200 PA), Díaz’s absurd 50.2 K% for 2022 is unmatched. By K-BB%, Díaz (42.6%) also bested every other relief pitcher by a wide margin (9.9% above Adres Muñoz’s 32.7%).
Díaz’s K-BB% being unrivaled is a measure of his propensity for mowing down whoever he faced, considering his BB% (7.7%) left him tied for a pedestrian 68th among qualified RP. Simply put, Díaz was largely untouchable during his historic campaign. But understanding precisely how untouchable can be derived by each underlying, absurd Plate Discipline metric of Díaz’s.
Díaz’s In Zone Contact% (63.2%), Out of Zone Contact% (26.8%) comfortably bested every qualified pitcher (minimum 200 PA) during his absurd campaign. Further contextualizing how absurd each aforementioned Plate Discipline metric of Díaz’s was can be done by examining how each has stacked up among every qualified pitcher since 2016 (again, minimum 200 PA).
Since 2016, using a larger seven-year sample size, Díaz’s Out of Zone Contact% of  26.8% would emerge unmatched. Moreover, Díaz’s Out of Zone Contact% has been unequaled by a very comfortable margin considering the sample size. 2018 Shohei Ohtani produced a 31% Out of Zone Contact%, which is a comfortable 4.2% behind Díaz’s from 2022. 
Also since 2016, Díaz’s In Zone Contact% has been bested only once, by Josh Hader in 2019 (61.7%) and by only 1.5%. Predictably, Díaz’s Whiff% (49.9%) from his historic campaign was also unmatched and is unrivaled by any qualified pitcher’s individual season over a shared seven-year sample size (comfortably above Hader’s 45.2% from 2019).
When using any previously mentioned metric, one characteristic which should be considered is how “contact” is extremely broad, and the quality of contact is overlooked. That being said, Díaz comfortably led each qualifying RP by both SwStr% and CSW% by a wide margin during his campaign. 
Each is a simple metric (SwStr% = each Swing + Miss divided by Pitch Total; CSW% = each Called Strike + Whiff divided by Pitch Total), and each is useful for providing a considerable K% correlation. But for a metric that has such a very simple and ordinary calculation, Díaz’s performance by SwStr% (24.7%) and CSW% (42.1%) was simply extraordinary. 
Since 2004 when Brad Lidge produced a 25.1% SwStr%, Díaz’s mark of 24.7% has been unmatched over a much unprecedented 18-year stretch. Furthermore, Díaz’s 42.1 CSW% is completely unrivaled by any qualifying RP since Lidge produced his aforementioned SwStr%.
Those who faced Díaz slashed .160/.230/.216, a far cry from .258/.332/.502 during 2019. His much-improved performance was reflected by his BB profile, and he conceded only 3 HR (15, 2019). Another drastic decrease was seen via his 4.1% Brl/BBE% (10.1%, 2019), 1.7% Brl/PA% (5.1%, 2019) and 9.4% HR/FB% (26.8%, 2019). 
Moreover, Díaz’s xwOBA, xBA, xSLG, and xISO placed him in the 100th percentile. Since 2017, his xwOBA (.202) has only been exceeded by Jacob deGrom’s mark of .190 from 2021. Díaz was clearly masterful, in avoiding contact altogether or limiting detrimental contact. 
Díaz entirely contradicted his measurable impact (or lack thereof) from 2019. If 2019 was indicative of Díaz’s worst, 2022 depicted his best. Díaz produced 3.60 WPA (-1.75, 2019) and 2.05 WPA/LI (-1.11, 2019) while being credited with 34 SD and only 3 MD (12, 2019).
The question is, what changed for Edwin Díaz between 2019 and now? One undeniable change Díaz made during his historic campaign was via his pitch usage.
Díaz has always utilized a two-pitch arsenal, which has consisted of a powerful 4-Seam Fastball and a devastating slider. Not once did Díaz’s 4SFB usage dip below 60.9% from 2017 through 2021, while his slider usage hovered between 31.3% and 37.8%.
However, a drastic usage swap came in 2022. During Díaz’s 2022 campaign, his total pitch count was 928 – 539 via slider (58.1%) and 389 via 4SFB (41.9%). From only a year prior, Díaz’s 4SFB usage decreased by 19.7% (61.6%, 2021) while his slider usage increased by 20.3% (37.1%, 2021).
The fundamental change was embodied by when Díaz used each pitch. Whether Díaz was ahead or behind, he showed continued preference toward his slider. While ahead, Díaz was 63.9% slider. While behind, preference continued, going 51.7% slider. When the count was full? 96.6% slider. 
By being ahead and staying ahead, Díaz could completely unleash his devastating pitch. And Díaz was frequently ahead – his First Strike% of 71.4% trailed only Chris Martin’s 77.8%
Díaz’s dominance wasn’t a byproduct of slider usage but instead ensued because of how much of a force his slider was. For example, Díaz’s slider produced a Run-Value of -22. Among every qualifying pitcher (minimum 150 PA) and every pitch type, Díaz’s -4.1 RV/100 was unmatched.
By slider only, Díaz’s RV/100 was above each and every peer by a comfortable margin (Andres Muñoz, -3.0). The electric pitch also very much exceeded every qualifying pitcher’s pitch type by PutAway% (rate of a two-strike pitch resulting in a strikeout). Díaz’s slider generated a 38.4% PutAway%, 5.5% above David Peterson and his slider’s trailing mark of 32.9%.
Díaz’s slider by K% (54.3%) and Whiff% (54.7%) was also unmatched by any qualifying pitcher (minimum 150 PA). His slider’s 54.7% Whiff% is a huge uptick from Díaz’s from what was generated during his disastrous 2019 when his pitch mustered a much lower 43.0% Whiff%. More distinctly depicting Díaz’s slider’s dominance during his historic campaign versus his poor 2019 is his wSL/C (Weighted Slider Runs per 100 pitches).
Díaz posted a 3.81 wSL/C of 3.81, demonstrating how impactful his pitch was while comparing his -0.76 wSL/C from 2019. The pitch produced a .114 BA, .134 SLG, and .154 wOBA – each signifying another unmatched mark among every pitch type by every qualifying pitcher (minimum 150 PA). Comparatively, Díaz’s slider from 2019 conceded a quite absurd .297 BA and .622 SLG.
The usage change, combined with the pitch’s potency, contributed toward Díaz producing a more drastic change in Whiff% (14.8) and In Zone Contact% (-11.8) than any other pitcher.  Only Andrew Heaney (-17.9%) saw a more drastic change in Out of Zone Contact% than Díaz did (-14.8%)
Out of Zone sliders represented 32.4% of Díaz’s 928 pitches in 2022. On such pitches, Díaz generated 141 Swings of which 114 were Misses, contributing 65 of his 118 SO. Furthermore, such pitches produced 80.9 Whiff% and 78.3 K%, while generating a 0.56 BA and .134 wOBA. 
In 2022, Díaz’s slider averaged 90.8 mph and touched 94.4 mph. Among the qualifying pitcher’s sliders (minimum 200 thrown), only Jacob deGrom (92.6 mph) and Emmanuel Clase (91.9 mph) produced a faster slider, on average.
Despite Díaz’s put-away pitch being inarguably impactful, Vertical and Horizontal Movement are far from a predominantly contributing factor. By a typical Stuff+ model, Díaz can be found a considerable one standard deviation above average (100 being average, each 50 equaling one standard deviation), but below a peer group of which he has produced favorably.
That being said, discounting Díaz’s dominance because of a pedestrian characteristic would be misguided. Tweaking his usage, everything aligned for Díaz while producing statistical dominance that any relief pitcher would envy. Even when Díaz didn’t have his best, he dug deep into a limited but impactful arsenal and did his job.
A useful example came during a memorable early September showdown versus Los Angeles. “Narco” blasting, Díaz entered in the eighth for New York, tasked with protecting a minimal lead. After walking Freddie Freeman, Will Smith received four consecutive sliders from Díaz – and was hit by the fourth. Max Muncy proceeded by driving a Díaz slider into deep RF for a long F9, and Justin Turner by driving another into deep CF for a long (402 ft.) F8.Unrecognized was Díaz’s profound pivot. After Turner turned on an 88.9 mph Díaz slider and almost tied the game, Díaz quickly changed his approach. He dialed up three consecutive 4SFB, each between 99.4 and 99.9 mph for Gavin Lux. Now ahead 1-2, Díaz continued, unleashed his velocity, and got Lux swinging on a 102.8 mph 4SFB – his fastest ever.  
But Díaz’s alteration versus Los Angeles is far from discernible of his propensity for overwhelming whoever he faced, which is how his season should be presented. Instead, and more symbolic of Díaz’s season can be shown during a pivotal early October matchup versus Atlanta, and his overpowering of William Contreras, who was villainized by New York’s fanbase for using “Narco”, which Díaz popularized, for his own walk-up song.
Simply put, Díaz made quick work of Contreras, and only a three-pitch sequence was needed from Díaz. The sequence, which contained a 91.4 mph and 92.8 mph slider with a 100.4 mph 4SFB in between, visibly proved Contreras both overwhelmed and outmatched.
Staying true to a theme of Díaz’s historic campaign, he got Contreras swinging on an Out of Zone slider, making Contreras one of 118 who was no match for Díaz during his undeniably dominant 2022 season.
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