How Martín Pérez is getting strikeouts without improving his stuff

I’m starting to come to grips with being very wrong about this Red Sox team. There’s still a lot of season left to be played, but I saw this team as .500 at best in a reasonable world, and it’s safe to say they are better than that. Granted, I realize that this is not the first time I have been wrong, nor will it be the last. It’s part of the fun of sports, and at least in this case it’s the good kind of wrong where who you are rooting for is exceeding expectations.

For me, the biggest reasoning for my low expectations surrounded the rotation. A lot of that had to do with my expectations for health, or lack thereof, among the unit, and to this point they have been remarkably healthy. It’s impossible to project that going forward, but so far it’s been great. But it hasn’t been all about health. They’ve also exceeded my expectations performance-wise, particularly in the bottom half of the group. And if we’re talking about pitchers exceeding expectations performance-wise, we have to start with Martín Pérez.

Pérez didn’t have the lowest expectations from me coming into the year within this rotation (that would be Nick Pivetta) but I certainly didn’t see him as anything more than a decent number five, and I did scoff at the idea of “Pérez Day” being a thing people celebrated. Well, I’m now celebrating as well. There’s a fair argument to be made that Pérez has been the best pitcher in this rotation full stop. So far this season he has pitched to a 3.09 ERA with a 3.49 FIP through 11 starts, and he only seems to be getting stronger as the year goes on.

And really, it’s not even just the fact that he’s putting up those numbers, but also how he’s getting it done. Pérez defenders have always pointed to his batted ball profile as the selling point, as he has consistently gotten weak contact over the last couple of seasons since adding a cutter as the focal point of his arsenal. This season, though, it hasn’t been weak contact getting it done. He’s getting decently weak contact, coming in at the 63rd percentile in average exit velocity and right in the middle of the pack in hard-hit rate, per Baseball Savant, but that hasn’t really been anything too special. In fact, his .301 batting average on balls in play isn’t really a net positive at all.

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Instead, the lefty is actually getting by with improved strikeout and walk numbers, which is exactly the opposite from the kind of pitcher he’s been more recently in his career. So far this season, Pérez is walking only 7.3 percent of his opponents, the second lowest of his career and the lowest since back in 2013. Meanwhile, he’s striking out 21 percent of his opponents. That’s not necessarily a huge number in today’s MLB, but it’s the highest of his career. And it’s not even just that he’s getting these strikeouts. It’s that he’s doing it while not really missing bats.

Pérez has never really been one to miss bats, which you can probably tell by him having never struck out 21 percent of his opponents in a season before. But his whiff rate (again, per Baseball Savant) is actually down from the last two seasons. The same trend follows when you look at his individual offerings, of which the curveball is the only pitch that saw more than a full percentage point increase in whiff rate from 2020, and he throws the curveball less than 10 percent of the time.

So he’s getting strikeouts, but not missing bats, which in turn obviously has to mean he’s freezing more hitters and getting more strikes called than ever before. And that is exactly what is happening. Pérez is hitting the zone more than he ever has, with Baseball Savant showing him hitting the zone at a rate over 50 percent for the first time in his career. Hitters are yet to make the adjustment to this new zone-pounding way of life, however, and in fact have done the opposite. Batters are swinging at these pitches in the zone just 63 percent of the time this year, the lowest rate he’s ever induced and a rate about three percentage points lower than the league-average. It doesn’t seem like a big deal, but these things add up and they are resulting in an average strikeout rate (which, again, is a legitimate leap for Pérez) as well as a reduction in walks.

To dig a little deeper into it, I went to Savant’s zone profiles to see if I could discern where in the zone he’s throwing more and where he’s getting more looks. I didn’t find a satisfying answer to the first inquiry, but the second question appeared to have a more convincing answer. As you can see below in a comparison between last season and this season in terms of which pitches opponents are swinging at, it’s the bottom of the zone where these pitches are going by, and specifically on the arm side.

Looking at this, it makes it pretty clear that hitters are not swinging much at the changeup and the sinker. Him getting these called strikes on the changeup is especially helping his performance against right-handed batters, who have just a .306 wOBA against him so far this season. (wOBA is an all-encompassing offensive stat on the same scale as OBP.) The sinker, meanwhile, is working against everyone, and while his whiff rate from last season has stayed pretty much stagnant into 2021, is up from 15 percent to 29 percent.

I do still have some concerns with Pérez moving forward, largely surrounding batters adjusting to what we’re seeing here and putting more of these balls into play. Maybe they’ll result in some weaker contact, but pitches low in the zone can be hit hard in an era of uppercut swings. That said, you can’t argue with the results thus far, and if he’s commanding the very bottom of the zone with movement, which he’s done this year, it’s easier said than done to both pull the trigger at the plate and impact the baseball. I suspect there will be some regression coming at some point for Pérez, but this new zone-pounding version of the lefty is putting him way ahead of my expectations, and helping the team follow that same path.