wPDI for Relief Pitchers: Mid-August Update

Previously, I provided the mid-August Weighted Plate Discipline Index (wPDI) update for starting pitchers. We took a deeper look at some rookies and comeback players found atop the wPDI leaderboard. Players such as Brendan McKay, Zac Gallen and Dinelson Lamet were highlighted by their deceptive repertoire.

Now it’s time to tackle the relief pitchers.

You can find the definitions and indexes of wPDI in its introductory article, found here. Here is a quick reminder on what the six possible plate discipline outcomes look like:

Let’s take a look at the 2019 year to date wPDI leaderboards, for relief pitchers [minimum 15 IP]:

Let’s dive into some detail for a few of the players at the top of the wPDI leaderboard:

Andrew Kittredge (.401 wPDI)

Andrew Kittredge of the Rays, sits atop all of baseball with a .401 wPDI. Currently, he has a 3.33 ERA with 36 Ks in 27 IP – a K/9 of 12 (K% of 32%). ERA estimators show that he has been unlucky – his xFIP is at a much better 2.79. He also has a .358 BABIP, which might mean that his 1.30 WHIP could be even lower.

In terms of plate discipline outcomes – Kittredge excels in the ABC outcomes, which are the out of zone binary possibilities. Andrew is getting lots of swings and misses outside the zone, while limiting his called balls. His outcome A is the 3^rd best among relievers; the only players with a better outcome A are Ken Giles and JT Chargois.

JT Chargois (.395 wPDI)

Speaking of JT Chargois (.395 wPDI) – after finishing 2018 within the top 20 of relievers, JT once again finds himself in the elite wPDI discussion. After having a nice season last year with the Dodgers where he finished with a 3.34 ERA, Chargois has a 5.00 ERA in 18 IP this season. Like Kittredge, this may be also be the product of bad luck. JT’s SIERA is a robust 2.81, which more closely corresponds to his 1.17 WHIP. Chargois has increased his strikeout rate from an 11 K/9 in 2018 to a 13 K/9 this season.

Robert Stephenson (.380 wPDI)

With a .380 wPDI in 46 IP, Robert Stephenson is a plate disciple pitcher surprise. For Stephenson, his Outcome A is about as good as it gets. 13% of all pitches that he throws are out of the zone, swung on and missed. Stephenson also generates little contact in the zone (Outcome E) and throws few pitches out of the zone which are not offered at (Outcome C). He is an ACE wPDI pitcher!

Stephenson is currently sporting a 4.70 ERA, but wPDI thinks that he is due for a nice correction. Other ERA estimators concur. For example, his 2019 SIERA is over a full run lower at 3.57.

Ryan Pressly (.395 wPDI)

To me, the most impressive player on the leaderboard is Ryan Pressly (.395 wPDI), who was the 2018 MLB wPDI leader with a .401 wPDI. At a .395 mark this season, he is now sits as the 2^nd best player in all of baseball. I wrote about Pressly’s dominance back in June – and since that time, he has remained fantastic. Ryan has a 1.99 ERA with a 0.88 WHIP on the season. He has only given up 9 walks yet struck out 57 batters in the 45 innings that he has thrown. Pressly is an elite reliever in baseball over the past two seasons, especially after being traded from the Twins to the Astros. The Astros are incredible at getting the most out of pitchers these days.

Hector Neris (.386 wPDI)

Finally, we come to Hector Neris (.386 wPDI), who I have not spoken about at all this year. Prior to the season, it was unclear who would assume the closer role for the Phillies. Newly signed David Robertson and fireballer Seranthony Dominguez were the favorites to win the job. Had we looked at his wPDI, we might have given more thought to Hector Neris as the possible Phillies stopper.

Neris finished 2018 with a .378 wPDI, which was good for the 9^th best of all relievers. His ERA was an awful 5.10 last year, although that came along with the best strikeout rate of his career at 14 K/9. The luck pendulum has swung the other way in 2019, as Neris is sporting a 1.01 WHIP propped by a .240 BABIP. His true talent is likely somewhere in between the two seasons, but it is clear that he has the ‘stuff’ to close out games.

As for plate discipline outcomes, Neris excels at outcomes A, B & E. Outcomes B & E are the contact scenarios. What Neris is doing well at, is making sure that when a batter makes contact with his pitches – it is out of the zone. He still induces more contact within the zone, but it is only a 6% difference to the out-of-zone contact. Other pitchers who are similar in that regard include Sergio Romo, Evan Marshall and Pedro Strop.