wPDI for Starting Pitchers: Mid-August Update

Earlier this season, I introduced a new pitcher metric – Weighted Plate Discipline Index (wPDI). It is a way to aggregate the six possible plate discipline outcomes into one simple quantity. By using plate discipline data alone, wPDI highlights the percentage of deceptive/effective pitches thrown.

Some lesser known undervalued pitchers who were revealed by wPDI in 2018 included Domingo German, Marco Gonzales, Will Smith and Ryan Pressly. Of course, wPDI also confirmed stars such as Chris Sale, Jacob deGrom, Max Scherzer and Aroldis Chapman.

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 leaderboard, for starting pitchers [minimum 25 IP]:

Blake Snell sits atop the starting pitcher wPDI leaderboard [min 25 IP] at .383. Sale was already the 7th highest wPDI starting pitcher last season at .361. He has risen to even higher heights in 2019 before his injury.

Other notable recognizable names in the top ten include Chris Sale, Justin Verlander, Stephen Strasburg, Gerrit Cole, Mike Clevinger and Max Scherzer.

Mike Clevinger (.378 wPDI) makes this list at #3 mostly due to his high Outcome D & F components. He generates little contact within the zone; his pitches are either swung on and missed, or not swung on at all. In addition, his component E is the lowest for any starter in baseball (a good thing!). Clevinger is unbelievably effective within the zone.

A few other 2018 wPDI standouts still continue to shine in 2019. Luis Castillo, Patrick Corbin and Charlie Morton have rated highly now for two years in a row. Shane Bieber, Kenta Maeda and Domingo German have now further cemented their prominence in wPDI.

Here are the key individual plate discipline outcome performers for 2019:

• Outcome A – Blake Snell, Luis Castillo, Kyle Gibson
• Outcome B – Tommy Milone, Kevin Gausman, Hyun-Jin Ryu, Jacob deGrom
• Outcome C – Brendan McKay, Justin Verlander, Jameson Taillon
• Outcome D – Mike Clevinger, Justin Verlander, Lucas Giolito, Jacob deGrom
• Outcome E – Mike Clevenger Luis Castillo, Robbie Ray
• Outcome F – Felix Hernandez, Chris Sale, Aaron Nola

A few rookie performers to catch my eye this year include Brendan McKay and Zac Gallen.

Brendan McKay (.362 wPDI) has the lowest Outcome C of all starting pitchers. That is, as a percentage of pitches thrown, he throws the fewest would-be called balls. A large percentage of his overall pitches are thrown within the zone (44% Zone%). His ERA is currently at 4.55, but wPDI thinks he may be a tad unlucky. Some other ERA estimators concur including SIERA, which has him almost a full run lower at 3.66. Keep your eye on this Tampa rookie.

Zac Gallen (.366 wPDI), who was just traded to the Diamondbacks for prospect Jazz Chisholm is another rookie wPDI standout. He is currently enjoying a fantastic first taste of the big leagues. To date, he has pitched to a 2.40 ERA with a 1.14 WHIP. He has fanned 49 batters in just over 41 innings – a K/9 of 11. Gallen doesn’t excel at any one plate discipline outcome – he has a nice base in all 6 outcomes. Unlike McKay whose true talent might be better than his performance thus far – Gallen’s wPDI serves to confirm his exemplary rookie season.

One other notable pitcher is Dinelson Lamet (.352 wPDI). Lamet, who very recently came back from Tommy John surgery, has now thrown 30 innings this season for an ERA of 3.90 ERA. He has amassed 42 strikeouts in that span for a fantastic K/9 of 13. In terms of plate discipline outcomes, Lamet sports a deception profile. He excels at throwing pitches out of the zone for whiffs, while also not generating swings at pitches inside the zone. If you recall – prior to his injury, he was a flashy rookie thought of to have high upside. The best might yet to come for Lamet. He may be an undervalued asset heading into 2020.