Salvador Perez, Plate Discipline, & Lineup Protection


Mandatory Credit: Troy Taormina-USA TODAY Sports

You’ve probably noticed lately that Salvador Perez has been struggling offensively. After going 0-5 last night, Perez is currently mired in an 0-22 skid. He hasn’t gotten a hit since last Thursday in Houston, and he hasn’t drawn a walk since April 9th. That was literally weeks ago. His lack of walks has been a point of discussion among Royals fans recently, since Perez started out the season drawing so many of them in the first 8 games (8 walks in 29 plate appearances, to be exact).

That 8th walk was the last that Perez earned, which of course leads us to wonder why he’s gone without a walk in his last 50 plate appearances. What happened to Perez’s discipline?

One common theory I’ve seen suggests pitchers were working around Perez to get to the hitter behind him, one Mike Moustakas. Intuitively, this makes sense, considering how poorly Moose has hit this season. When Perez was moved up in the order, he didn’t draw any walks, so that seemed to confirm the hypothesis. Generally speaking, lineup protection isn’t something that has a significant impact in most situations, but perhaps there are specific instances in which a pitcher will give a more dangerous batter nothing good to hit.

Because this theory interests me, and because the data is readily available at FanGraphs, I decided to dig into the numbers to find out if pitchers were being more cautious with Perez while Moustakas stood in the on-deck circle. First, we must remember what needs to happen in order for a player to draw a walk:

1. The pitcher must throw several balls out of the strike zone, and
2. the batter must not swing at at least 4 of those pitches.

Knowing that, I wanted to look at two things:

1. How often did pitchers throw balls to Perez that were out of the strike zone when he was ahead of Moose, compared to when he was not?
2. How often did Perez swing at those balls out of the strike zone?

To find this information, I looked at the Pitchf/x Plate Discipline data from Perez’s game logs. Because the swing and zone percentages are, well, percentages, I also looked up the number of pitches Perez saw in each game. I broke every game into one of two groups: With Moose and Without Moose. Using the Zone%, I was able to determine the raw number of pitches Perez saw that were in and out of the zone, and I then used his O-Swing% to calculate the raw number of out-of-zone pitches he swung at in each game.

I could have tried to isolate a few other variables (pitch type, situation, specific pitch location, etc.) but breaking it down too far may just create too much noise. Plus, the sample isn’t overly large, so diluting it further wouldn’t provide much credibility to any conclusion.

Here are a couple of nifty charts showing the results.

[table id=1 /]

* These numbers do not match up perfectly with FanGraphs’ numbers, because pitches on an intentional walk do not register with Pitchf/x.

[table id=2 /]

As you can see, the numbers are quite telling. Not only have pitchers not been working around Perez to get to Moose, but they’ve actually thrown a higher percentage of pitches in the strike zone when Moustakas is up next compared to when someone else is on-deck. The difference isn’t significant, but the fact that it isn’t significant is kind of significant for this question. If pitchers were more concerned about being hurt by Perez than by Moose, they wouldn’t throw Perez hittable pitches.

So right away we see that the lineup protection theory once again goes out the window. And really, when you look even deeper, the theory has yet another massive hole. Most of the pitchers the Royals have faced this year have been right-handed, meaning that the pitcher would have a platoon advantage against Perez, and be at a disadvantage against Moustakas. While Perez has been a superior hitter to Moose in their careers, they aren’t terribly dissimilar when facing righties (Perez 92 wRC+, Moose: 89 wRC+).

Left-handed pitchers working around Perez to get to Moose would make much more sense, considering the massive gap in their production levels against southpaws (Perez: 151 wRC+, Moose: 61 wRC+). Indeed, Perez’s lone intentional walk came while facing a left-handed pitcher. However, Perez has only faced a lefty pitcher 18 times this season, and only a handful of those came with Moustakas in the on-deck circle, so it’s tough to draw too strong of a conclusion.

In general, though, Perez saw roughly the same percentage of pitches in the strike zone, whether Moustakas was up next or not. “Then why,” you surely wonder aloud, “why didn’t Perez draw any walks when he moved up in the batting order?”

If I can direct your attention to the far right column of both of the above tables, you’ll see the answer. If you don’t feel like scrolling back up, due to laziness or a defective mouse, I can repeat the information here.

With Moustakas hitting behind him, Perez has swung at 32.18% of pitches out of the strike zone. When Moustakas was not the hitter in the on-deck circle, Perez swung at 48.08% of pitches out of the strike zone.

It’s really as simple as that.

Early in the season, Perez was doing an excellent job of laying off pitches out of the zone. That coincided with the time when Moose was hitting behind him, but I don’t believe there is any kind of causal relationship there. To give you a better idea of why Perez has gone so long without drawing a walk, here’s a graph of Perez’s season-long O-Swing% following each game this season:

You’ll notice a bit of a trend there. As the season has progressed, Perez has gotten worse and worse at identifying which pitches to swing at and which pitches to let go. While Perez is a pretty good bad-ball hitter, he’s an even better good-ball hitter, so he would be best served to swing at the pitches with which he can drive with more authority. If he doesn’t get enough pitches in the zone, he can happily take first base.

If you include the intentional walk, as I’ve done above, Perez’s O-Swing% currently sits at 36.69%. Taking out the intentional walk results in an O-Swing% of 39.3%, which is a little higher than his career number of 37.8%. Since Perez has been pretty consistent in that rate, I’d expect to see it begin to normalize at some point, because even though he may swing too often, I can’t imagine he’ll continue swinging at over half the pitches out of the strike zone, as he’s done in 6 of the last 7 games.

Despite the claims of many, Perez’s early-season walks had far more to do with the player in the batter’s box than the player in the on-deck circle. Perez has brought this current slump on himself by swinging wildly so often, so it probably wouldn’t be a bad idea for Perez to get a day off soon. Beyond the team’s need to keep him healthy, Perez is hurting the offense right now, and giving him a day might help him return to something close to the level of plate discipline he showed earlier in the season, even if he doesn’t become a walking machine.