What Salvador Perez Does in the Shadow Zone

You know roughly what a good batter’s stat line looks like. Here’s Juan Soto’s league-leading 2020, for example: .352/.486/.703 with 20.2% walks and 14.8% strikeouts. In 2019, Mike Trout hit .291/.438/.645 with 18.3% walks and 20% strikeouts. These make sense as “good” in my head, even if I can’t calculate how many runs they were worth without looking it up. Salvador Perez has a 177 wRC+ in 140 plate appearances this year, one of the hottest streaks of his career, and he’s batting an unrecognizable .356/.371/.667. Huh?

Oh yeah — Perez is also walking 2.1% of the time this year while striking out in 20% of his trips to the plate. He has 10 homers and three (3) walks. He’s swinging at pitches outside of the strike zone 46% of the time, the fourth-highest rate in the majors. This is the plate discipline you’d expect from a light-hitting catcher, not from a guy who would have the third-highest wRC+ in baseball this year if he had enough playing time to qualify. We’re going to need an explanation here.

One look at Perez’s Swing/Take profile (courtesy of Baseball Savant) will get your regression senses tingling:

Perez swings at 70 percent of the pitches he sees in the shadow zone, the edges of the plate and the area just outside. Only five batters in the league have swung at more at pitches in that zone. He swings at 21% of pitches in the waste zone, the highest rate in baseball (league average is 5.5%). There are certainly productive hitters who swing a lot, but they usually do it by piling up value in the heart of the plate and living with the downsides. Perez creates more runs by swinging at borderline strikes and balls than he does by swinging at pitches down the pipe.

Jeff McNeil led the league in swing rate last year, and he also hit .318/.384/.531, good for a 143 wRC+. You can absolutely succeed while being aggressive. Take a look at McNeil’s Swing/Take chart, though:

This is how you succeed with aggression. Hit the ball with enough authority in the center of the strike zone and you can make up for the inevitable whiffs and poorly hit balls when the pitcher fools you. You do enough to spoil those shadow and chase pitches and you can make the whole package work, because every out-of-zone pitch you don’t swing at is an unqualified success. McNeil — who, again, swung more than any batter in baseball last year — accrued more value by taking than swinging. Javier Báez accrued more value by taking than swinging in 2019!

If we want to figure out what’s powering Perez’s weird 2020, we need to start looking at those shadow zone swings. Perez mostly fits the profile of a swing-happy hitter with good contact skills, aside from this one thing that turned him from his old self into a hitting demigod. What changed?

The first thing I wanted to check was whether we need to split Perez’s behavior in half based on the count. You could imagine a hitter who takes big, homer-happy swings at everything until there are two strikes, then chokes up, shortens up, and defends the plate to guard against strikeouts. In Perez’s case, there’s little evidence of that:

He swings at more pitches in the shadow zone with two strikes, as do all hitters as a whole — and he increases his swing percentage by roughly the same amount. But he doesn’t whiff any less with two strikes or hit more grounders; he’s actually hitting the ball hard more often with two strikes than without, though that could easily be a sample size artifact.

What’s truly remarkable is how well Perez fares when he puts the ball in play. The hard hit rates and wOBA values don’t make a lot of sense without context, but consider Perez’s numbers from 2015-18:

In essence, he’s trading extra whiffs for loud contact. The amount of loud contact he’s gaining, however, is off the charts. Take a look at the league as a whole in 2020:

From 2015-18, Perez was a swing-happy-but-otherwise-unremarkable hitter in the hazy area at the border of the strike zone. He made up for the extra swings by missing less often, and the whole package worked out reasonably. In 2020, he’s missing slightly more often, but he’s also putting up the best numbers of his career and hitting the ball hard far more often while he does so.

In isolation, the fact that Perez massively increased his contact quality on hard-to-hit pitches looks like a fluke. It looks even more like a fluke when you consider his position in the league as a whole:

Perez is fourth in baseball in wOBA on contact in the shadow zone, and he’s first overall in xwOBA. He’s 22nd in barrel rate on those same pitches, which is worse but still impressive. That doesn’t mean this power is here to stay — xwOBA is more descriptive than predictive — but the underlying numbers don’t show any truly worrying signs.

One way to get a juicy xwOBAcon number is to hit a ton of flares, balls that carry over infielders but fall in front of outfielders. Because of the way it’s constructed, xwOBA values those balls highly. Hit something at that angle and speed, and it will almost always be a hit. It’s not a particularly repeatable skill, though; hit the ball a little harder or softer, or a little lower or higher, and your expected outcomes fall off a cliff. That’s why barrels are the predictive statistic of choice; miss a barrel by a little bit, and you’ll have an exceptionally hard-hit ball in the air. The near-barrel zone is a much better place to live than the near-flare zone.

Perez is hitting more flares out of the shadow part of the strike zone this year than he ever has before, but it’s not a wildly unsustainable number. Statcast classifies 27.1% of those batted balls as “flares or burners,” only a hair above the league average of 24%. His 10.2% barrel rate outstrips the league’s 5% rate by more, and that’s what we really care about. If we’re looking for a reason to doubt him, we’ll need to find something else.

You might wonder about the quality of Perez’s opposition. The pod-style regular season leads to uneven competition in general, and Perez has played an abbreviated season, which could make this effect even more extreme. Maybe he just faced an easy slate of pitchers!

The only problem with that idea is that it isn’t true. Perez’s opponents have compiled a 4.34 FIP (weighted by how many times they faced him) and a 4.28 xFIP. They’ve struck out 24.8% of opponents while walking 8.9%. For those of you keeping score at home, each of those is better (for the pitchers) than league average.

Same swing rate, reasonable opposition, wildly better results? It doesn’t stack up. But there’s something hidden in the numbers that at least partially helps unpack the change. Perez, like most batters, is a fastball hitter. He’s produced 24 runs above average on his career by hitting fastballs, which sounds underwhelming until you add context: he’s produced -18 runs on sliders and -22 on curveballs.

That counts all pitches; whiffs, takes, fouls, and balls in play. But even if you look only at the balls in play, he’s far better against the hard stuff; he’d hit for a .391 wOBA against fastballs and .312 against breaking pitches. One problem: he didn’t do a great job at identifying what was what, particularly in that pesky shadow zone. From 2015-19, he swung at 64.6% of fastballs and 63.3% of breaking balls around the edges of the zone.

This year, he’s swinging at 70.4% of fastballs and only 63.6% of breaking balls. That might not sound like much — and honestly, it isn’t! It’s seven extra swings at fastballs, give or take, in the 140 plate appearances he’s made so far this season.

That’s not enough to matter! Seven swings? Perez has been 13 runs above average this year with the bat, which brings his career total to zero runs above average. Seven swings at fastballs doesn’t come close to explaining that.

I’d argue that all of these things together — swinging harder, doing more damage when he connects, using his aggression around the borders of the plate to his own benefit, identifying better pitches to swing at — are merely the result of one thing changing: Sal Perez is healthy again.

Before the 2019 campaign, Perez had Tommy John surgery. That isn’t terribly common for a catcher, but Perez strained his flexor tendon while preparing for the season. As Jay Jaffe chronicled, catchers have a poor return rate from TJ, though the last two names on the list — Christian Vázquez and Travis d’Arnaud — hint at potential better outcomes in recent years.

Perez was hardly healthy in previous years, too. In 2018, he missed the first 20 games of the season with an MCL strain, then caught 129 of the remaining 142 games on the schedule. From 2014 to 2017, he caught 4488 innings, the most in baseball, and that excludes two extended postseason runs. Simply put, he sustained a workload that no other catcher attempted for four years, then he spent two years injured.

This year, Perez has caught a healthier complement of games; he’s 22nd in baseball in innings behind the plate. He’s only that low due to a stint on the IL, the result of a freak fluid-filled particle in his left eye. That sounds awful, and it surely is, but from the standpoint of catching, it’s less worrisome than arm or lower body injuries. It’s hardly a surprise that Perez has a history of hitting better in the first half than the second; catchers as a whole display that split, and Perez catches a heavier slate of games than most.

There are a host of reasons that Perez’s current form won’t continue. He’s 40th in the league in overall barrel rate, which would both be his best finish on that leaderboard and not nearly high enough to sustain his current production. He walks too little, and regardless of what Statcast says about his expected batting average (.359), he’s simply not going to keep that kind of production up. He’s a catcher with a .388 BABIP, and that won’t keep going. Batters get hot sometimes, and that doesn’t mean that they’ll never fall back to their previous form. Heck, Perez has even had stretches like this before in 2013 and 2016:

I wouldn’t bet on Perez to continue this form next year because he’ll almost surely follow his previous pattern, which is to play as much as he can on the way to eventually wearing down. He’s already making a start on it: when the Royals offered players the chance to stay after the season for a training camp, Perez was “eager for the extra work.” Given a chance to take it easy, he seems intent on continuing to keep hustling.

Don’t let the uncertain future distract you from the present, though. Right now, Salvador Perez is feeling good and playing well. His aggressive approach at the plate means that we’re noticing the results of his hot streak more often; he’s not powering himself with walks, but rather roped line drives and home runs. What Perez is doing in the shadow zone is almost certainly not sustainable; he’s swinging at the same pitches, more or less, and simply turning them into gold instead of lead. But that doesn’t mean it’s not fun to watch right now.

Note: All stats current through games of September 23.