At the present moment, Edwin Díaz ranks first in the MLB in reliever WAR. On May 1st, I wrote an article discussing how Edwin Díaz had changed. At that time, he was behind Josh Hader and Adam Ottavino in WAR. Now, despite only pitching 6.2 more innings, Díaz leads Ottavino by 1.0 WAR, and leads Hader by a not-insignificant 0.4 WAR.
Before I was skeptical because it’s rather easy to fall prey to small sample sizes. Díaz had surely been dominant, but it had just been a month or so, and his 2017 was certainly more mediocre than elite.
Yet here we are, July 10th, and Díaz is among the top of most leaderboards in which you would like to see him leading. In xwOBA (expected weighted on-base average), Díaz is second only to Josh Hader. In actual wOBA, Diaz ranks sixth. In xFIP, Díaz is first. In SIERA, Díaz is second (by only one point!). In K/9, Díaz is fourth.
As I was taking a peek at QOP Baseball, I was surprised to find that Díaz’s fastball and slider both ranked incredibly low in terms of quality. How could someone who has been so elite not have quality pitches?
According to FanGraphs, Díaz has one of the best sliders in the league.
FanGraphs’ leaderboard falls in line with what most people believe of Díaz’s slider: it’s good! More specifically, it’s the 11th best in the MLB.
According to QOP Baseball, this is how Díaz’s slider ranks in the following categories:
- Rise: 57th percentile
- Late break: 47th percentile
- Horizontal break: 5th percentile
- Vertical break: 29th percentile
- Location: 21st percentile
- Velocity: 97th percentile
- 3.36 QOPA (quality of pitch average; 4.50 is league average)
For QOP Baseball, their logic is that a good pitch will rank highly in many, if not most, of these categories. Díaz only fares well in velocity. If you hadn’t seen him pitch and only looked at these metrics, you would think he’s a mediocre fireballer.
QOP Baseball does have a point. Díaz’s slider is pretty subpar in terms of movement, and his velocity is very high for a slider.
Here is a table of the top 11 sliders in baseball (per FanGraphs), mostly in order:
Díaz’s horizontal movement is well below average (even with McHugh single-handedly swaying the mean), and his vertical movement is relatively average. However, he does have the fastest slider of the group by more than 1.0 mph.
This seems like an oversimplified method of measuring the quality of a pitch. Or maybe it’s not! Like QOP Baseball says: it’s measuring the quality of a pitch, not the value of it.
Other than velocity, location, and movement, there are other methods to set yourself apart as a pitcher. Here is where Díaz does just that:
Pitch tunneling is an increasingly popular concept that suggests that the longer two different pitches travel within the same path, the more effective they will be. That seems incredibly intuitive — and it’s likely a reason why Felix Hernandez was successful for so many seasons: his changeup looked like his fastball, until it didn’t.
So if you see a hitter swing at a Díaz slider like this, you’ll know that it must have looked like his fastball:
A more straightaway view may give a better glimpse into how utterly ridiculous it must be to try and hit against Edwin Díaz:
To further visualize this, we will compare Edwin Díaz and Juan Nicasio’s fastball-slider combos to one another.
First, a bird’s-eye view visual:
You can see that Nicasio’s pitch trajectories diverge earlier, and are wider later.
A side visual:
This is just another vantage point, but again, you can see that immediately Nicasio’s fastball-slider trajectories are not intersecting. For Díaz, they are intersecting for the first five or six points.
It still isn’t entirely clear why Díaz has taken such a gigantic leap forward since 2017. As I’ve suggested before, his slider has gained a 1.0 mph uptick in velocity. He’s stopped throwing his two-seam fastball as much in favor of his four-seam. He’s increased slider usage. His release point has changed.
Regardless of what is precipitating his success (which is almost definitely the return of his slider), he’s a major reason the Mariners have had so much success this season. When you have a closer as dominant as Díaz, you’re going to win close games, and boy have the Mariners won more close games than they should have. Edwin Díaz is on pace for 3.2 WAR, and the Mariners are 6.0 games ahead of the Athletics in the Wild Card race. For now, all is well. There’s not a better way to slice it.