Introducing: The Maddux Plate Discipline Index (mPDI) for Pitchers

“The key to pitching is to have the ability to throw a strike when they’re taking and throw a ball when the hitter is swinging.” – Greg Maddux

Last week, I introduced a pitcher metric based on the six possible plate discipline outcomes. You can find the definitions and indexes in the wPDI introduction article, found here.

This week, I would like to provide you with an alternative weighting of the indexes. It will parallel the famous quote by Hall of Fame pitcher, Greg Maddux. He preached that the key to pitching is to throw a strike when the batter isn’t going to swing, and to throw a ball when the batter will [swing].

With the wPDI outcome framework in place, we can now properly quantify Greg Maddux’s quote.

Here is a quick reminder on what the six possible plate discipline outcomes look like:

Maddux Plate Discipline Index (mPDI) for Pitchers:

The formula for mPDI, the Maddux Plate Discipline Index:

mPDI = Index_A * A% + Index_B * B% + Index_C * C% + Index_D * D% + Index_E * E% + Index_F * F%

A%, B%, …, F% is defined exactly as in wPDI – the percentage of total pitches per each outcome.

The mPDI indexes are given as:

Since the indexes for A, B, F are all 100%, and with C, D, E% all set to 0% – we can simplify the Maddux Plate Discipline Index (mPDI) as:

mPDI = A% + B% + F%

There we have it! This formula exemplifies Maddux’s key to pitching as the aggregate of three simple quantities. It represents the total percentage of outcomes where the batter either swings at a “ball” [Outcomes A & B] or looks at a “strike” [Outcome F]. We obviously know that pitching is a bit more complicated, but it’s a marvel to quantify a legend’s words.

mPDI tops out at around .400 for the elite, and bottoms out at roughly .200. The average for mPDI is lower than that of wPDI and comes close to .300. That is, roughly 30% of the time – pitchers are implementing Maddux’s key to pitching.

Let’s see the 2018 leaderboards for mPDI:

Patrick Corbin leaps over Chris Sale to sit atop the starting pitcher mPDI leaderboard. As previously noted, Corbin excels at outcome A – generating swings and misses out of the zone.

Kyle Hendricks now jumps up to the #2 spot due to his elite F outcome – he generates few swings within the zone. 19% of his pitches fall into this category.

Southpaw Marco Gonzales leapfrogs up to the #5 slot. He excels at outcome B – getting batters to make contact out of the zone.

Jason Vargas ahead of Jacob deGrom? Do the Mets have something special with their 5^th starter?

According to mPDI, in 2018 Vargas had fantastic plate discipline in the Maddux categories. Vargas did a better job than deGrom at pitching in the zone without generating a swing. While the overall out-of-zone metrics were in deGrom’s favor – Vargas fared a shade better at initiating the out-of-zone contact.

On the reliever side, not a whole lot has changed when going from wPDI (with my prior indexes) to mPDI. Aroldis Chapman moves down a bit – he excelled at outcome E, which isn’t factored in as much with the mPDI weights. Ryan Pressly, who I talk about here, also dazzles.

Alex Claudio is one reliever that caught my eye. Claudio excels at the A & B outcomes – the out-of-zone pitches. It seems that mPDI may have a small tilt towards lefties, as we have seen several of them bubble up to the top.

Below are the players with the largest gaps between mPDI and wPDI:

Bartolo!!!

Bartolo Colon (still active) throws a ton of strikes. It always amazed me that batters let so many of his pitches go by without a swing … knowing that so many pitches were simply mid-80 MPH fastballs in the zone.

Here are the players that dropped the most when switching to the Maddux indexes:

This list contains a large number of hard throwing relief pitchers. Hader’s best asset is his category D outcome. It is a swinging strike in the zone. Hader has more than double the major league average D outcome – which factors greatly for wPDI, but not for mPDI. Hader gets almost as many swings and misses in the zone as he gets called strikes in the zone. Interestingly and somewhat surprisingly, Hader’s mPDI is below average at .297. Edwin Diaz though (another elite reliever), still has a fantastic mPDI at .332.

Hader isn’t a mediocre pitcher. It is quite the opposite – he is elite. Hader’s plate discipline skills are just not what Greg Maddux had in mind.