FanPost

Does Plate Discipline Matter?

USA TODAY Sports

In my last post on the struggles of Yoenis Cespedes, I made the case that Cespedes' variations (small I might add) in plate discipline are not a large factor in the performance drop from 2013 vs. 2012. A lot of the comments suggested that I glanced over the differences too lightly. So I thought I would dig into the matter a little more deeply.

I ran a linear regression model against plate discipline on 698 hitters from 2000 until 2013 (plate discipline stats aren't available before 2000). I ran the plate discipline stats for correlation against every offensive category. Below is the data. (if you want to see all the plots, go here)

A little background. O-swing is the percentage of pitches out of the strike-zone a batter swings at. O-contact is the percentage of pitches out of the strike-zone a batter swings at and makes contact. Z-swing is the percentage of pitches in the strike-zone a batter swings at. Z-contact is the percentage of pitches in the strike-zone a batter swings at and makes contact.

Linear regression shows how strong a set of data can be represented by a straight-line. For the data below, I show two values: the r2 and coefficient. The r2 value corresponds to how well a line represents the data. Zero is a terrible fit, one is a perfect fit. The coefficient is the slope of the line, as in y = mx+b. The coefficient is the slope, or m. For example, say a set of data has an r2 value of .8 and a coefficient of 10. That means the data is well represented by a line (.8) and has a strong dependence on the variable (10).


OPS

OPS

HR

HR

AVG

AVG

BB%

BB%


Rsq

Coeff

Rsq

Coeff

Rsq

Coeff

Rsq

Coeff

O-Swing

0.021334

-0.175719

0.000059

-10.021932

0.000265

-0.005266

0.344052

-0.253627

Z-Swing

0.026056

0.218331

0.036769

282.474002

0.001213

0.012677

0.055523

-0.114551

Swing

0.014279

-0.196365

0.000393

35.483822

0.000013

0.001567

0.424816

-0.384965

O_Contact

0.036423

-0.129274

0.01637

-94.390557

0.090233

0.054757

0.073718

-0.066101

Z_Contact

0.069737

-0.441019

0.052596

-417.140229

0.129464

0.161709

0.082134

-0.172024

O-Contact_div_O-Swing

0.000047

0.000672

0.008932

-10.035454

0.043308

0.00546

0.136997

0.01297

Z-Contact_div_Z-Swing

0.053327

-0.113771

0.060097

-131.541957

0.020205

0.018846

0.001815

0.007544

Z-Contact_div_O-Contact

0.01582

0.035226

0.001018

9.734726

0.053505

-0.017434

0.050727

0.022672


K%

K%

BB_K

BB_K

OBP

OBP

SLG

SLG


Rsq

Coeff

Rsq

Coeff

Rsq

Coeff

Rsq

Coeff

O-Swing

0.029642

0.139306

0.347776

-2.011276

0.193944

-0.189868

0.000245

0.013858

Z-Swing

0.024581

0.142623

0.095617

-1.185679

0.022592

-0.072857

0.085785

0.291367

Swing

0.005198

0.079683

0.328069

-2.668343

0.221724

-0.277305

0.004472

0.080824

O_Contact

0.349892

-0.269478

0.066978

0.496966

0.000519

-0.005531

0.061722

-0.123771

Z_Contact

0.71858

-0.952137

0.182205

2.020909

0.00022

0.008868

0.134239

-0.45003

O-Contact_div_O-Swing

0.292536

-0.035466

0.575468

0.209673

0.154187

0.01372

0.033006

-0.013028

Z-Contact_div_Z-Swing

0.242359

-0.163125

0.175613

0.585295

0.014563

0.021307

0.139056

-0.135122

Z-Contact_div_O-Contact

0.167052

0.076988

0.022368

-0.118746

0.001243

0.003539

0.023718

0.031723


BABIP

BABIP

wRCplus

wRCplus


Rsq

Coeff

Rsq

Coeff

O-Swing

0.007833

0.030193

0.011021

-32.44824

Z-Swing

0.002156

-0.017811

0.000921

10.546182

Swing

0.001767

-0.019591

0.045625

-90.180507

O_Contact

0.00067

0.004973

0.006371

-13.89066

Z_Contact

0.004317

-0.031115

0.042298

-88.242624

O-Contact_div_O-Swing

0.004077

-0.001765

0.001993

1.118129

Z-Contact_div_Z-Swing

0.000099

0.001391

0.012201

-13.981491

Z-Contact_div_O-Contact

0.001872

-0.003437

0.000271

1.184201

Now I will take a stab at breaking down each category.

OPS

Plate discipline's effect on OPS is minimal at best. The strongest correlation is with Z-Contact, but with a negative impact. Keep in mind OPS is less than one, so the coefficients have good weighting, but on a poor fit.

HR

Not much correlation here. Z-contact is the highest, but again at a negative impact. Presumably this is the impact of Juan Pierre-type players.

AVG

This one isn't so bad. We get a pretty good relationship between Z-contact and AVG, with a decent coefficient (remember AVG is less than 1). We also see swinging and making contact outside of the zone isn't a death sentence to batting average.

Walks

Not bad. Second best fit of any group. Swinging at pitches results in less walks. Duh.

Strikeouts

Best fit! Again, duh. Making more contact results in less strikeouts.

BB/K ratio

Some decent fits here. Plate discipline seems to play a role in walks and strikeouts.

OBP

The best fit is Swing% with a negative impact. Free swingers seem to have a lower OBP. Who would have thought?

SLG

The best fit is with Z-Contact, but with a negative impact. Damn you Juan Pierre!

BABIP

Positively the worst fit of any group. I would be comfortable saying any small deviations in Cespedes' plate discipline are not affecting his BABIP. I was a little surprised on this one. I thought swinging at better pitches might result in better hit balls for a higher BABIP, but not the case.

wRC+

Finally. We see the best (and still not good) fit is what negative impact free swinging has. But overall not any good fits to draw any real conclusions on.

Conclusion

While I don't hold a PhD in Mathematics, I think the take-away from this is that predicting performance on plate discipline ALONE year-to-year is ill-advised. It is possible over a significant portion of at-bats you could draw a conclusion Player A may get more walks or strikeouts than Player B based on plate discipline, but the correlation numbers are just too small to predict any significant batted-ball differences in the short term. So while I am not thrilled that Cespedes is making contact at 4% fewer pitches in the strike zone, it is nothing to sit and cry about.

In other words: Cespedes! Fix your swing not your pitch selection!

(apparently your BP/HR Derby swing is fine.)

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