Weighted Plate Discipline Index (wPDI): 2019 Review

In my previous article, I gave an update on my Weighted Plate Discipline Index (wPDI) metric. wPDI arises from the core ingredients of plate discipline – looking only at zone rates, swing rates and contact rates.

An important distinction regarding wPDI, is that its sample size is quite a bit larger than other statistics. Many other stats are based on innings pitched, or even per plate appearance. The denominator of wPDI is pitches. While batter outcomes such as strikeouts and walks stabilize fairly quickly, wPDI can work even faster.

Let’s now take a look at the 2019 leaderboards for wPDI, to see if we can find some undervalued players.

Starting Pitchers

Above is the 2019 wPDI leaderboard for starting pitchers.

Blake Snell lead all starting pitchers in wPDI in 2019. The key to Snell’s success was his “out of the zone” plate discipline. In particular, Snell’s Outcome A (out of the zone, swung on and missed) was the 2^nd highest of all qualified pitchers in baseball. In 2019, Blake produced a K% rate of 33.3%, the highest of his career. He logged a whopping 147 strikeouts in just 107 innings pitched. Both FIP and xFIP (3.32 & 3.31 respectively) agree that his 4.29 ERA last year was somewhat unlucky.

The health of Snell is a concern for fantasy owners, but if healthy – Blake Snell is a very undervalued asset, as substantiated by wPDI.

One elite wPDI pitcher to point out is youngster Zac Gallen. Gallen was traded mid-season from the Marlins to the Diamondbacks, swapped for prospect Jazz Chisholm. After dominating AAA earlier in the year with a 1.77 ERA, 0.71 WHIP and a K% of 33.6%, Gallen continued to shine at the major league level. He struck out 96 batters in 80 innings, compiling a sparkling 2.81 ERA along the way.

Looking at Gallen’s plate discipline makeup, in contrast to Snell – it is his “in the zone” outcomes which make him elite. He had one of the highest Outcome F rates of any starter (in the zone, no swing), and a low combined total of Outcome D+E. In short – for pitches in the zone, he is generating few swings, and otherwise little contact.

Gallen still has more to develop. His walk rate rose starkly in the majors upon his promotion. He was a tad lucky last year with a .284 BABIP and an 84% strand rate, so expect his ERA to rise in 2020. All things considered, his deception and plate discipline give us a hope for continued success. Take a flyer on this wPDI maven.

Relief Pitchers

Here are the top wPDI relief pitchers of 2019:

In 2019, Ryan Pressly led all of Major League Baseball in wPDI at .401! Do you know who led the MLB in wPDI in 2018? None other than Ryan Pressly with a .401 mark as well! After two years of dominance, it is clear that the Astros pitcher has developed to an elite reliever.

What does Pressly do well? Everything! His Outcomes A (out of zone, swing and miss) and F (in-zone, no swing) are super-elite. Getting swings and misses out of the zone, and generating called strikes are the keys for deception and “stuff.” From March to May last year, in his first 26 innings, Pressly yielded only one earned run. He only issued just two walks in that span. Incredible!

Roberto Osuna might have a lock on the closer role in Houston, but Pressly is every bit as good, if not better. In this short season, Pressly could get save opportunities, and will most certainly help your fantasy squad’s ratios. Consider owning him in mono leagues, in deeper mixed leagues, and even in some 12-team formats. He won’t be expensive to purchase.

I mentioned above that Blake Snell had the 2^nd highest Outcome A of all major league pitchers. Finishing at the top of the Outcome A list, and high up on the overall 2019 wPDI RP leaderboard is Reds reliever, Robert Stephenson.

There are so many aspects of Stephenson’s game to like. The former first rounder had nearly a 20% swinging strike rate last year, generating a 31% K% rate. His out pitch is his dominant slider, which he throws more than half of the time. Stephenson was somewhat lucky last year; his BABIP was a very low .230, but that does not affect his wPDI. Keep your eye on this surging Reds reliever.

Other honorable mentions at the top of the wPDI RP 2019 leaderboards include Josh Hader and Adam Morgan. Hader, we all know about – but I would like to call your attention to Adam Morgan. Morgan generated a ton of swings out of the zone (Outcomes A & B), and was able to get an elite number of called strikes (Outcome F).

Year on Year Risers

Let’s take a look at the pitchers exhibiting the most improvement in their plate discipline metrics. Below are the biggest risers in wPDI for starting pitchers from 2018 to 2019 (min 40 IP in 2019):

With his splitter, Frankie Montas was the single greatest wPDI gainer for starting pitchers. Montas exhibited a pitch mix change from year to year, which is likely the core of what led to his large jump. From wPDI’s view, Montas is a sleeper for 2020.

Lucas Giolito follows on the list, jumping into star territory. I am hopeful that those gains can stick in 2020. Monitor him in his first few starts to see if his wPDI has fully translated.

Here are the largest relief pitcher gainers from 2018 to 2019:

Jimmy Cordero, who has bounced around a few organizations, finally found it on the South side of Chicago. On the White Sox, Cordero pitched to a 2.75 ERA and a 0.97 WHIP in 36 innings last year. A .387 wPDI is worth monitoring.

Another White Sox player – Evan Marshall, kicked up his wPDI into high gear. Marshall, who previously had little success in the major leagues, finally had some at the age of 29. He threw 50+ innings of 2.49 ERA ball. Perhaps the White Sox front office reads my column?

Check out Andrew Kittredge of the Tampa Bay Rays. The Rays felt confident enough to trade bullpen stud Emilio Pagan to the Padres this offseason, and Kittredge could be one of those reasons. In 49 IP in the majors last year, he struck out 58 batters – a K/9 of 10.5. He compiled a 4.17 ERA, but FIP/xFIP say that it was unlucky (3.56/3.25, respectively). His BABIP was also a high .336. He was fantastic in AAA before this year’s call-up. In the minors last year, he threw 37 innings for a 1.93 ERA and an 0.80 WHIP, with a staggering 55 strikeouts (13.2 K/9). In this short season, keep a close and early eye on Kittredge for save chances, and how he develops.