Lucas Erceg’s Changeup Will Take Him Far

As Gunnar Henderson stepped to the plate in the bottom of the ninth inning of Game 2 of the AL Wild Card Series on Wednesday night, his team down by a run and one out from elimination, it felt like something special was brewing. Late-inning tension, high stakes, one of the sport’s biggest stars: The postseason was peaking, and the young superstar held the Orioles’ fate in his hands, poised to deliver a signature moment. Unfortunately, he had to deal with Lucas Erceg’s changeup.

Lucas Erceg, Filthy 91mph Changeup. ?

Royals Advance. ? pic.twitter.com/kWKQQy0gzZ

— Rob Friedman (@PitchingNinja) October 2, 2024

I’ve followed Erceg all year, first from afar, mystified by the flamethrower that materialized out of nowhere in the Oakland bullpen, and then with a closer eye when he moved to Kansas City, watching him slip seamlessly into the fireman role in the Royals bullpen. His eye-popping fastball velocity caught my attention, but it’s the changeup stealing the show on the bright October stage.

As the table shows, Erceg’s velocity sits at the top of the scale. His four-seam fastball averages 99 mph. Again, he sits at 99 mph. But the results on it were just so-so: It graded out at 0.1 runs per 100 pitches by Baseball Savant’s run value calculations, neither helping nor really hurting him.

I think the pitch’s performance can be explained by its exceedingly “normal” shape. (Shout out to Leo Morgenstern.) Erceg throws his fastball from a 43-degree arm angle, which is smack dab in the tall part of the histogram among major league pitchers. From that bog-standard arm angle, his fastball gets roughly league-average induced vertical break.

Max Bay’s “dynamic dead zone” application projects how batters might perceive Erceg’s fastball relative to arm angle expectations. While the pitch drifts further to his arm-side than batters might initially expect, the vertical expectations are basically identical. The conventional shape of his four-seam fastball knocks it down a peg from a “stuff” perspective, taking it from plus-plus to maybe just plus.

But a high-velocity fastball doesn’t exist in a vacuum — it exists in the context of all in which it lives and what came before it. In other words, it impacts all of the other pitches in an arsenal. As Erceg rears back to throw, hitters have to keep that 99 mph in mind. And that expectation will certainly help a changeup play up.

The velocity separation between his four-seam fastball and changeup is solid — Erceg’s changeup averages 91 mph — but the horizontal movement of the pitch is its most distinct quality. It averaged 17.9 inches of horizontal movement this season; of the 165 pitchers who threw at least 150 changeups in the regular season, only three averaged more horizontal movement, putting Erceg in the 98th percentile.

Some of that arm-side fade is seam-shifted-wake effects; some of it is connected to Erceg’s motor preferences. (Mario Delgado Genzor wrote a great primer on motor preferences for Baseball Prospectus in January.) Erceg, as far as I can tell, is a pronator, which means that his natural throwing motion is conductive to changeups that run and fade to the arm side. Watch how he whips his forearm toward his body in the slow-motion part of this video:

Lucas Erceg, Wicked 91mph Changeup. 🤢

19 inches of run. pic.twitter.com/pUOkcCQ91Z

— Rob Friedman (@PitchingNinja) October 1, 2024

In these playoffs, at least, it’s been not just the movement that’s exceptional, but his pinpoint command of the pitch. On that 1-2 changeup to strike out Henderson, he buried it in that perfect location right below the knees, where it looks like a low fastball right up until the point that it isn’t.

What makes one changeup better than another is generally one of the more difficult questions to answer in pitching analysis. Royals ace Cole Ragans, for example, had one of the best changeups in baseball this season. Its effectiveness can’t really be explained by its shape — it doesn’t have much depth or movement differential from the fastball. But hitters, time and again, swing through the pitch, deceived by Ragans’ arm action or the way the trajectory mirrors his fastball or some other variable that is impossible to measure. Unlike a fastball, a changeup cannot be easily graded by a stuff model because it depends on how it plays against the expectations of the fastball.

What makes Erceg’s changeup good, however, seems pretty obvious to me. It goes fast and it moves a ton, almost like a lefty slider.

The changeup helps Erceg stand above other relievers with more limited arsenals. Against righties, he is mostly a sinker-slider guy, throwing his two-seamer in on the hands and then dropping his slider below the knees for whiffs. But against lefties, he relies on his four-seamer and changeup, neutralizing lethal lefties like Henderson. The results bear this out — Erceg faced roughly an equal amount of righties and lefties this season and held them both in check (.242 wOBA against righties, .279 wOBA against lefties).

There is a flip side to extreme pronation: It is hard to throw big, sweepy glove-side breaking balls. And yet Erceg’s slider has actually graded out as his best pitch by run value and whiff rate this season. As Erceg’s pitch movement plot shows, befitting his pronation bias, the slider doesn’t actually get any glove-side movement, coming awfully close to achieving a true “deathball” shape. Note the yellow dots representing the sliders he threw this season:

Even without glove-side movement, that shape can still be super effective. When Kumar Rocker made his debut, some analysts were throwing 80 grades on his “deathball” slider. Erceg’s slider is shaped just like Rocker’s, but Erceg throws his a couple miles an hour harder.

Erceg’s top-end velocity, platoon-neutral arsenal, and rapidly improving command (a 14.3% walk rate in 2023, an 11.9% walk rate when Michael Baumann wrote about him in May, and a 4.4% walk rate since that post) suggest to me that he could make a transition to starting pitching. Even if he drops two or even three miles per hour while stretching out to six-inning appearances, the fastball velocity will still be well above average. And if the Royals do decide to go that route, they could accrue significant benefits without risking too much. According to Roster Resource, they have him under team control through the rest of the 2020s, giving them plenty of opportunity to reverse course if it doesn’t work out.

Lucas Erceg, quality major league starter — it’d be quite an ending to a remarkable story. He was drafted by the Brewers as a third baseman in 2016, but after struggling to hit in the high minors before and after the pandemic, Erceg made the switch to pitching. Just 18 months ago, our lead prospect analyst Eric Longenhagen wrote that “his mechanical inconsistency impacts his fastball location,” but noted that Erceg had a “chance to make a consistent big league impact if things click for him command-wise.” He is still so new to this, and so it is easy to imagine what could be.

But all of that is for the future. Right here, right now, in the heart of the playoffs, Erceg is the primary weapon out of a surprisingly solid Kansas City bullpen. And it’s the changeup, in my view, that is setting him apart.