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Yainer Diaz Has Developed Improved Plate Discipline: Does It Really Matter?

Unruly or disciplined, he still rakes

MLB: Houston Astros at New York Yankees
 Dusty Baker Jr. (12) slaps hands with catcher Yainer Diaz (21) after his three run home run during the first inning against the New York Yankees 
Vincent Carchietta-USA TODAY Sports

Watching the too few games in which Yainer Diaz partakes, I’ve lately noticed fewer swings at bad pitches, especially ones above the zone.

That could just be my lying eyes, so I checked it out.

It's true.

But before we look at the data on Diaz’s improved plate discipline, let’s chuckle at a few fun facts about the underused rookie phenom.

Yanier Diaz Fun Facts

Yainer Diaz hits a home run every 18 PAs. Yordan Alvarez hits one every 16, and Kyle Tucker every 22. But when Diaz catches, he hits a home run every 13 PAs. In his 12 prime years, Johnny Bench, the Babe Ruth of catchers, hit a home run every 21 PAs. Bench’s career wRC+ was 125. In his rookie year so far, Diaz is hitting 118 wRC+. But as a catcher, it’s 178, and he’s improving slightly as the season progresses. Clearly, if Yainer Diaz gets to play more, he will be the greatest catcher of all time. (That’s a joke, folks)

Yanier Diaz Plate Discipline Numbers

OK, enough of that; back to the subject at hand. Is Diaz’s plate discipline improving, and does it mean his overall production is improving?

Let’s look at the chart below.


Yanier Diaz Plate Discpline o-swing% z-swing% swing% o-contact% z-contact% contact% sw strike%
Yanier Diaz Plate Discpline o-swing% z-swing% swing% o-contact% z-contact% contact% sw strike%
3/30-7/7 50.4 77.6 60.9 65.4 85.6 75.3 15
7/8-8/8 43.9 83.2 60.4 48.3 84.8 69.3 18.5

Interesting. Diaz’s o-swing percentage has dropped about 7%. That means he is swinging outside the zone much less. On the other hand, his z-swing% is higher, meaning he is swinging at more of the pitches inside the zone. Both those trends indicate improved plate discipline. He is swinging less at pitches he shouldn’t swing at and more at pitches he should swing at.

But how much is it working for him?

Yanier Diaz Contact Numbers

While swinging wildly at balls outside the zone, his o-contact% was 65.4%. That’s high for pitches outside the zone. For comparison, the gold standard for plate discipline and contact hitting, Alex Bregman, only swings at 22.1% of balls outside the zone but makes contact on 73.9% of those.

Now Diaz’s o-contact% has gone down to 48.3%. His contact inside the zone is about the same as it was. And while swinging at fewer balls outside the zone by a large measure and more balls inside the zone, somehow Diaz’s swinging strike percentage has gone up from 15% to 18.5%.

In general, better selectivity for Diaz has had the counter-intuitive result of reducing his overall contact rate from 75.3% to 69.3%.

So how about the results?

Has Improved Plate Discipline Helped Diaz’s Production?

Diaz has been generally well above league average and remarkably consistent throughout the season. But with what most would say is an improving approach, you’d expect more significant improvement.

Here is his slash line plus other stats for March 30 through July 7.

.272/.281/.509... 112 wRC+.....237 ISO.....278 BABIP....BB% 2.2....K% 18.7....Hard Hit % 46.9

And here are the stats for the last month

.274/.309/.516....121 wRC+....242 ISO.....265 BABIP.....BB% 2.9.....K% 16.2...Hard Hit% 37.7

So, in the last month, we see a small improvement in results, but nothing dramatic considering the sample size of 68 PAs. The on-base percentage is up slightly, wRC+ is up slightly, the base on-ball percentage is up slightly, and the strikeout percentage is down slightly. All just slightly. Notice a drop in hard-hit %. Possibly more discipline means less aggressiveness. Hopefully, this new style is the beginning of even bigger improvements yet to come as Diaz adjusts to his new style of hitting and develops the perfect balance of aggressiveness and discipline.

Let’s look at some heat maps to see what these adjustments are.

What Adjustments Has Diaz Made?

This is Diaz’s swing chart for 3/30-7/7.

As I said at the outset, I noticed that Diaz loved to swing above the zone, and here it is. Now let’s look at Diaz since July 7.

Notice that Diaz is swinging a lot less above the zone and in the high side of the zone and a lot more at low pitches in and low. It’s like the coaches are telling him to lay off the high heat.

Now let’s look at the results.

A Look At Diaz’s Recent Hitting Profile

Here’s the SLG% heat map for the pre-July 8 part of the season.

Pretty impressive, but note that the high end of the zone and the quadrants just above the zone are areas of relative strength. He swung at the high pitches with success. But two quadrants above the zone, Diaz was hitting zero, and he was swinging at a lot of those pitches. Pitchers were getting him to miss those, but they had to be sure not to come too low.

Here’s his chart post July 7.

Now, Diaz can’t seem to hit the high quadrants much. Or outside the zone nearly as well as before, either. But he is raking low inside and middle-high, outside in the zone offerings.

Diaz’s Future

It has all pretty much evened out for Diaz, this new plate approach, and in the long run, it will probably reap benefits. But for now, not swinging at high pitches as much has had the paradoxical result of him not hitting as many of the ones he does swing at, including the ones inside the zone he should and did swing at and hit.

But it all bodes well. He is still a very raw hitter. Swinging at high pitches worked for him in the minors. It probably won’t work for long in the majors. He has shown a willingness and ability to adjust and has made significant adjustments quickly. Which means he has a lot of growth ahead. Starting from such a strong rookie baseline, that is extremely encouraging.

The future is bright for Yainer Diaz. If he ever gets to play much.

Let Yainer Diaz Play Catcher

C’mon Dusty. Catching Maldonado 80% of the time makes about as much sense as not touching the chalk when you go out on the field. I don’t care if the pitchers think he’s a lucky charm. They mostly resisted the shift, too, back in the day. They’ll get used to a catcher that provides run support.

Oh yeah, Diaz threw out three out of three base stealers yesterday, had a homer, a single, and two RBI—another day at the ballpark. Johnny Bench, watch out. Dusty Baker, get out of the way.