The Mets’ 2020 bullpen and the Edwin Diaz dilemma

According FanGraphs’ Steamer system, the 2020 New York Mets are projected to have the top bullpen in the National League and the third-best relief corps in all of baseball with an even 5.0 fWAR. That’s a seemingly preposterous notion to a fan base that suffered through a season sunk by what was, for large parts of the year, a historically bad bullpen. If your immediate reaction was to scoff at the absurdity of it all, you’re not alone.

Still, it was easy to be fairly high on the Mets’ relievers heading into the 2019 season. The team traded for dominant closer Edwin Diaz, re-signed formerly dominant closer Jeurys Familia, and added Justin Wilson to a bullpen that already included stud Seth Lugo and the (usually) dependable Robert Gsellman. It looked pretty good on paper, anyway.

There were plenty of reasons that last season’s bullpen was such a disaster. Injury, poor performance, lack of depth, bad bullpen management, lack of starter length early in the season, and plain bad luck are just a few that can reasonably be applied to the 2019 Mets’ beleaguered bullpen. Perhaps the singular most relevant reason for the collapse, however, is also a most clichéd baseball adage: bullpens are volatile.

First-year general manager Brodie Van Wagenen looked to make a splash in a now infamous move that traded some of the Mets’ future for win-now reliever Diaz and win-yesterday second baseman Robinson Cano. It’s hard to imagine how the trade could have turned out any worse considering both players flopped, but the floundering Diaz will likely have the bigger impact on the success (or failure) of the 2020 Mets.

By now you’ve seen multiple analyses that center on Diaz’s poor 2019 performance from the outcome perspective (increased HR rate, walks, etc.), and we’ll definitely touch on that a bit further in this article. As a change of pace, though, this piece focuses more on the execution and behavior of his pitches in an attempt to identify any key differences between 2018 and 2019 that may have led to such contrasting results.

There’s understandably been a lot of chatter about his slider and its ineffectiveness this past season, but his fastball was noticeably worse in 2019 as well. You’d be hard-pressed to find a more striking example of the consequences of a two-pitch reliever losing both of his weapons, and the situation was made all the worse for Diaz as a newly-acquired, high-profile player in the New York market.

The table below presents various data points pertaining to Diaz’s arsenal (his four-seam fastball and slider) for both 2018 and 2019. The information is sourced from Statcast and Pitch/FX data from multiple sites, including FanGraphs, Baseball Savant, and Brooks Baseball. I’ve also included a scatter plot from Brooks Baseball below the table that depicts the average movement of his pitches in 2018 and 2019. This is in an effort to provide a bit more context for the positive and negative numbers associated with pitch movement and release points, and there’s a short primer at the end of this article providing additional detail*.

	2019 FS	2018 FS	2019 SL	2018 SL
Spin Rate	2371	2341	2367	2377
H-Move(in)	-7.04	-5.96	0.97	1.17
V-Move(in)	7.91	8.9	2.72	2.4
Velo	97.8	97.9	89.8	89.7
V-Release(ft)	5.14	5.31	5.35	5.45
H-Release(ft)	-2.93	-2.76	-2.85	-2.7
HardHitRate	47.50%	36.90%	42.60%	32.70%
FB%	30.77%	26.19%	29.79%	18.75%
HR	9	2	6	3
BAA	.237	.188	.333	.121
K%	41.50%	32.90%	35.90%	56.40%

The first things to note are that the spin rate on his four-seamer ticked up by 30rpm and both the horizontal and vertical movement changed fairly significantly. That 30rpm may seem insignificant, but keep in mind that even a difference of 100rpm at high velocities can impact swinging strike percentages significantly. Oddly, the upward vertical movement on his four-seamer actually decreased rather than increased with the higher spin rate. You’d typically see the reverse, where more backspin leads to an increase in the “rise” of a four-seam fastball. There’s a difference of a full inch here, which is considerable for a game where mere millimeters mean the difference between a home run and a pop fly. The change in horizontal movement on his fastball also indicates an increase in sidespin, causing it to cut more into right-handers and away from lefties. These differences could indicate a slight change in his grip, where the pitch acts a bit more like a two-seamer but is still clearly a four-seam fastball.

It’s likely that his slower slider wasn’t affected as much by the smaller 10rpm decrease in spin rate, though with this pitch its horizontal movement would be impacted more by changes in the spin rate. We can see that there’s less than an inch of difference in vertical and horizontal movement on the pitch between 2018 and 2019, though it’s worth pointing out that it had more lift and less break away from right-handers than it did in 2018. Again, small differences can have huge consequences.

The changes in the release point for both pitches were included in the table because it’s an interesting data point, and I thought perhaps inconsistencies here may have been a potential cause of his bad fortune. Though he had a slightly lower, flatter release point for both pitches in 2019, it really is negligible. As an aside, I plotted both pitches by month for 2018 and 2019 in the charts below, and he’s actually been remarkably consistent.

So what does all of this get us besides a closer look at some cool Statcast and Pitch/FX data? Well, at the very least we can see that some of his mechanics have remained consistent between 2018 and 2019. It’s a bit of a stretch to believe that the slight changes in the behavior of his pitches led to the carnage that was his 2019 in Queens, but hitters were clearly locked in when he took the mound. This is evidenced by the sample of outcome metrics in the table that really drive home just how thoroughly Diaz was thrashed last season.

The hard hit rate for each of his pitches in 2019 was astronomical and averaged out to 45.3%, which was in the bottom 2% of the MLB. Statcast also has a statistic known as Barrel, which essentially leverages exit velocity and launch angle to identify how many times a batter “squares up” on a pitch. Unsurprisingly, Diaz’s 10.1 Barrel% was in the bottom 8% of the MLB last season. The huge increases in his fly ball rate, home runs allowed, and batting average against are well known at this point, but they’re quite stark when compared to the small changes in his pitch behavior.

If we consider that his 2019 pitches acted very similarly to their 2018 counterparts, and there was no dip in velocity, then we’re left with questions centered on things like his ability to hit his location, pitch tipping, sequencing, and just plain bad luck.

It’s difficult to analyze differences in the sequencing of his pitches and the predictability of the choices he and his battery mate made in any given at bat, though it should be noted that he only leaned on his four-seamer slightly more often in 2019 than he did the season before. Likewise, and while still a possibility, it would be surprising if he was tipping his pitches and we have yet to hear about it. Still, the authority with which hitters demolished his offerings and the roughly 10% increase in their pull rate against him sure make it seem like they had a good idea of what was coming. In terms of luck, attributing his ills to the cruel fates certainly seems like a cop out, but the .377 BABIP that hitters tallied against him combined with the almost 10% increase in contact on his pitches outside the zone sort of bear that line of thinking out a bit.

What does Diaz need to fix and how does he do it? Is there actually something that needs fixing? It may be that the Mets eventually do identify the cause for his down year and he makes the appropriate corrections heading in 2020, but it’s possible that we already identified the primary cause many paragraphs ago. Relievers are a fickle bunch, and it’s perfectly reasonable to believe that Diaz had a 58-inning blip that was more catastrophic to his team’s fortunes than most sample sizes that small.

Returning to the premise of our headline, the dilemma the Mets are presented with is whether or not to hand Diaz the closer role at the outset of the 2020 season and make it his to lose. With a year in the New York spotlight under his belt, and the hope for a regression to the mean regarding luck, do they bank on him getting back on course as the anchor for what has the potential to be an elite bullpen? Or do they hand the reins to someone like Lugo and make Diaz earn it back like he did in Seattle in 2017? For what it’s worth, I’m of the opinion that you plug Diaz in as the closer and remove him if he once again plays himself out of that role. Only, you know, do it sooner.

It might be hyperbolic to state that the success of the Mets’ 2020 bullpen depends on which version of Diaz manifests itself next season, but it’s not that far from the truth. As we saw this past season, it only takes one failing cog to throw the entire machine into disarray. A healthy and effective quartet of Lugo, Familia, Diaz, and the newly-acquired Dellin Betances could certainly make that projection a reality, but there are many “ifs” involved in reaching that ideal scenario. Can Diaz and Familia regain their form? Will a healthy Betances come close to resembling his former, dominant self? Will the time bomb that is Lugo’s elbow continue to hold up?

That 5.0 fWAR projection would absolutely look nice on the Mets’ bullpen this season, but before we start counting those chickens we should remember that Steamer was pretty high on the Mets’ bullpen in 2019 as well. What did the projection gods foresee before last season for Mets relief pitchers? Second in the NL and third in the MLB with an fWAR of 4.3. Of course, they just missed the mark on that one by landing at a robust 0.7 fWAR. Relievers, man.

* The X and Y axes intersect at the center with a value of zero. The perspective is from the catcher’s point of view with the intersection acting as the center of home plate. Negative numbers on the Y-axis represent downward movement, while positive numbers represent upward movement. Likewise, negative numbers on the X-axis represent pitches moving towards a right-handed batter while positive numbers represent pitches moving away. The locations of the bubbles are relative to the center of the chart and do not represent where the pitches landed within the strike zone.