When Plate Discipline Sticks

A few days ago, Jake Leech asked me if Zack Cozart’s 2017 improved plate discipline would stick into 2018.


Cozart saw quite a bit of improvement with his K%-BB% dropping by 6% points.

Note: I like using K%-B% to get an overall value for a hitters plate discipline. Earlier this year, I investigated what early season stats point to a true breakout. K%-BB%, along with launch angle (FB%), were the two key factors to focus on.

Zach Cozart’s Plate Disciple
Season BB% K% K%-BB%
2016 7.3% 16.5% 9.2%
2017 12.2% 15.4% 3.2%
2018 (Steamer) 8.8% 15.6% 6.8%

The Steamer projection has his K%-BB% regressing closer to his 2016 values than the ones from 2017. This is how projections work with previous season stats having some weight along with some regression.

From the Tweet thread, I wondered if some underlying plate discipline values (Pitch Info swinging and contact values using inside and outside rates) could point to a hitter keeping more of the gains.

I took all the hitters (min 200 PA) since 2008 who saw their K%-BB% increase by 7.5% in one season and then their eventual value in year three. I started with hitters who saw a 6% change like Cozart. I couldn’t find a nice year-to-year trend. I did find one at 7.5%. The 6% values generally lined up but the 7.5% values were more obvious.

Once I found the hitters who improved their plate discipline, I grouped the hitters by who kept the improvement going forward into three groups. Here are the results.

Note: To make sure the results weren’t from the largest changes regressing the most, I found the year one to year two changes. The average changes were within 0.3% (8.6%, 8.9%, 8.7%) of each other.

Keeping Plate Discipline Indicators
Average O-Swing% Z-Swing% Swing% O-Contact% Z-Contact% Contact%
Kept Changes -2.4% 0.1% -2.4% 8.0% 3.9% 4.9%
Regressed Some -1.5% -0.5% -1.5% 3.8% 2.4% 3.0%
Heavy Pullback -0.9% -2.0% -1.9% 5.8% 1.8% 3.4%
Median O-Swing% Z-Swing% Swing% O-Contact% Z-Contact% Contact%
Kept Changes -2.3% 0.1% -1.6% 6.8% 3.9% 5.1%
Regressed Some -2.2% -0.6% -1.8% 3.8% 2.4% 3.1%
Heavy Pullback -1.3% -2.5% -2.2% 5.3% 2.0% 3.0%

The two categories which showed consistent progression were O-swing% (outside swing rate) and Z-contact% (strike zone contact rate).

With these two findings, I went down several paths such as combining their values and performing regression. In the end, I kept the values separate and decreased each a bit to a 2% point drop for O-swing% and a 3.5% increase for Z-contact%.

I found all the hitters with at least a 7.5% point drop in K%-BB% with the 2%/3.5% change (Good Indicators group). Then I compared them to the rest with the 7.5% drop (Bad Indicators).

Plate Discipline Indicators At Work
Year1 Year2 Y2 – Y1 Year3 Y3 – Y2
Good Indicators 16.3% 7.2% -9.0% 9.4% 2.2%
Bad Indicators 16.1% 7.0% -9.0% 11.1% 4.1%

Both groups saw some regression but the good indicator group didn’t regress as much. Examining the results from 2016 to 2017, five players fall into the Good Indicators group who should keep most of their gains for 2018.

Hitters Most Likely to Keep Major Plate Discipline Changes
2016 2017 Difference
NAME PA K%-BB% O-Swing% Z-Contact% PA K%-BB% O-Swing% Z-Contact% K%-BB% O-Swing% Z-Contact%
Steven Souza Jr. 468 27.4% 32.1% 76.0% 617 15.4% 24.9% 79.4% -12.0% -7.3% 3.4%
Eddie Rosario 354 22.3% 44.3% 79.4% 589 12.1% 40.2% 81.9% -10.3% -4.2% 2.5%
Joey Votto 677 1.8% 23.2% 84.7% 707 -7.2% 18.4% 88.5% -9.0% -4.8% 3.8%
Marwin Gonzalez 518 18.5% 36.9% 89.1% 515 9.7% 28.8% 91.1% -8.8% -8.2% 2.0%
Anthony Rendon 647 8.0% 27.6% 87.3% 605 -0.3% 20.1% 91.8% -8.4% -7.4% 4.5%

Two stars and three breakouts from last season are on the list. Here some quick thoughts on each:

  • Joey Votto: He is the league’s closest thing to a hitting robot. He took the league’s best plate discipline to a whole new level. Good luck pitchers.
  • Anthony Rendon: He transitioned from a .270/.350 (AVG/OBP) hitter to borderline elite one at .300/.400. Even if he regresses some, the high OBP and power will keep him accumulating counting stats.
  • Steven Souza Jr.: The changes transformed him from borderline unplayable to a decent sleeper. The one issue to remember is that he’s more valuable in an OBP league with his sub-.250 AVG.
  • Marwin Gonzalez: I’m afraid his value going to jump as he is qualified at 1B, SS, and OF. Also, it helps that he’s productive and everyone saw him in the postseason.
  • Eddie Rosario: I see why owners might not buy in but he had his 2017 breakout season with his BABIP dropping from .338 to .312. He’s being more selective at the plate and driving the new juiced ball all over the field. Believe.

Getting back to Cozart, he just didn’t meet the criteria to keep his changes into 2018. He’ll keep some but as his Steamer projection shows, he’s likely to see his plate discipline pull back. Instead, players making and keeping plate discipline changes need to start with a notable plate discipline change along with the ability to lay off pitches out of the strike zone and hit the pitches in it. Basically keeping the improvement comes down to: don’t swing at balls and hit strikes.

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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6 years ago

I am so confused on the blurb about Marwin. Perhaps it needs some editing?

6 years ago
Reply to  kev1nchoi

Makes sense to me. Increased value for multiple positions plus he got a lot of added attention because of the postseason.