Saturday Study Hall, Vol. 5
Analyzing both pitchers and hitters using plate discipline metrics
Saturday Study Hall is a biweekly series defining advanced stats, data and analytics to investigate how they impact the Royals.
Plate discipline — we talk about it a lot, especially as it pertains to young hitters ascending from the minor leagues to the Majors. After any given plate appearance or game, you’re likely to see or hear chatter similar to “this pitcher is wild” or “that hitter swings at everything.”
Unfortunately, those discussions are often derivatives of the eye test or subjective analysis. Guess what? There’s easily accessible data available to test those hypotheses! Big shocker, I know.
Measurements of both hitter and pitcher skill like O-Swing and Z-Contact fill the pages of this site and many others. If you find yourself puzzled by the plate discipline data that litters modern baseball discussions, this condensed Saturday Study Hall session is for you.
Let’s start by defining the foundation of these statistics. “Z” refers to inside-strike zone and “O” refers to outside-strike zone. Ah, simplicity.
One other caveat to keep in mind as you explore these statistics on your own: There are multiple providers of them, and because the strike zone itself can be a bit subjective based on the source of the data, it’s important to choose one source and stick to it so your analysis is consistent.
For example, under the Pitch-Level Data tab on FanGraphs, you’ll find Sports Info Solutions, Statcast and Pitch Info all providing their own versions of plate discipline metrics. Personally, I opt for Statcast since so much of my other work stems from Baseball Savant, which is powered by Statcast.
To be clear, those three sources are all going to return similar enough results. Salvador Perez is going to show a high O-Swing rate in all of them (especially over the last couple weeks…), but the exact number may differ slightly. Just something to keep in mind as you conduct your own research: Don’t use Sports Info Solutions to dig up a pitcher’s O-Swing rate then jump to Statcast to find his Zone rate. Keep it consistent.
With that quick caveat out of the way, let’s jump into the definitions for the most common plate discipline statistics you’ll find cited throughout baseball discourse. These metrics can be used inversely for both hitters and pitchers.
Zone Rate or Zone%
Percentage of pitches inside the strike zone. (In-zone pitches divided by total pitches.)
Z-Swing Rate or Z-Swing%
Percentage of pitches a batter swings at inside the strike zone. (Swings at pitches inside the strike zone divided by pitches inside the strike zone.)
Z-Contact Rate or Z-Contact%
Percentage of contact a batter makes on swings at pitches inside the strike zone. (Contacted swings divided by swings on pitches inside the stroke zone.)
O-Swing Rate or O-Swing%
Percentage of pitches a batter swings at outside the strike zone. (Swings at pitches outside the strike zone divided by pitches outside the strike zone.)
O-Contact Rate or O-Contact%
Percentage of contact a batter makes on swings at pitches outside the strike zone. (Contacted swings divided by swings on pitches outside the strike zone.)
Contact Rate or Contact%
Percentage of contact a batter makes on all swings. (Contacted swings divided by total swings.)