When Gunnar Henderson entered the game in the bottom of the ninth inning of Game 2 of the AL Wild Card Series on Wednesday night with his team one run and one lead from elimination, it felt like something special was brewing. Late-inning excitement, high stakes, one of the sport's biggest stars: The postseason was at its peak and the young superstar held the fate of the Orioles in his hands and was poised to deliver a defining moment. Unfortunately, he had to deal with Lucas Erceg's move.

Lucas Erceg, Filthy 91mph Changeup. ?

Advance of the Royals. ? pic.twitter.com/kWKQQy0gzZ

— Rob Friedman (@PitchingNinja) October 2, 2024

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

As the table shows, Erceg's speed is at the top of the scale. His four-seam fastball averages 99 miles per hour. Him again sits at 99 miles per hour. But the results were only mediocre: Baseball Savant's run value calculations showed he averaged 0.1 runs per 100 pitches, which neither helped nor really hurt him.

I think the performance of the pitch can be explained by its exceedingly “normal” shape. (Shoutout to Leo Morgenstern.) Erceg throws his fastball from a 43-degree arm angle, which is right at the top of the histogram among major league pitchers. From this standard arm angle, his fastball gains a vertical break that is about league average.

Max Bay's Dynamic Dead Zone application projects how hitters might perceive Erceg's fastball relative to arm angle expectations. While the pitch travels further to his arm side than hitters would initially expect, the vertical expectations are basically identical. The conventional shape of his four-seam fastball flips it many times over from a “stuff” perspective, changing it from “plus-plus” to perhaps just “plus.”

But a high-velocity fastball doesn't exist in a vacuum – it exists in the context of everything it lives in and everything that came before it. In other words, it impacts all other pitches in an arsenal. As Erceg retreats to throw, the batsmen must keep the 99 mph speed in mind. And this expectation will certainly help bring about change.

The velocity difference between his four-seam fastball and his changeup is solid — Erceg's changeup averages 91 mph — but the horizontal movement of the pitch is its most noticeable quality. Horizontal movement averaged 17.9 inches this season; Of the 165 pitchers who made at least 150 changeups during the regular season, only three on average moved more horizontally, putting Erceg in the 98th percentile.

Some of these fades on the arm side are seam shift effects; Some of this has to do with Erceg's motor preferences. (Mario Delgado Genzor wrote a great introduction to motor preferences for Baseball Prospectus As far as I can tell, Erceg is a pronator, meaning his natural throwing motion results in transitions that fade and fade toward the arm side. Watch him pull his forearm toward his body in the slow motion portion of this video:

Lucas Erceg, Wicked 91mph Changeup. 🤢

19 inch barrel. pic.twitter.com/pUOkcCQ91Z

— Rob Friedman (@PitchingNinja) October 1, 2024

At least in these playoffs, it wasn't just his movement that was exceptional, but also his precise command of the court. On that double changeup to strikeout Henderson, he buried it in the perfect spot just below the knees where it looks like a low fastball to the point where it isn't.

What makes one change better than another is generally one of the most 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 difference from the fastball. But hitters keep swinging around the pitch, fooled by Ragans' arm movement or the way the trajectory reflects his fastball or some other variable that can't be measured. Unlike a fastball, a changeup cannot be easily evaluated through a stuff model because it depends on how it performs against the expectations of the fastball.

However, what makes Erceg's move good seems pretty obvious to me. It's quick and it moves big, almost like a lefty slider.

The move helps Erceg stand out from other substitutes with more limited arsenals. Against righties, he's mostly a sinker-slider guy, throwing his two-seamer to his hands and then dropping his slider below his knees to sniff. But against lefties, he relies on his four-seater and his changeup, neutralizing lethal lefties like Henderson. The results prove this: Erceg faced roughly the same number of right-handed and left-handed hitters this season and kept both in check (.242 wOBA vs. right-handed hitters, .279 wOBA vs. left-handed hitters).

There is a downside to extreme pronation: it is difficult to throw large, sweeping, glove-side breaking balls. And yet, Erceg's slider actually turned out to be his best pitch-by-run stat and whiff rate this season. As Erceg's pitch motion chart shows, in keeping with his pronation tendency, the slider actually receives no movement on the glove side, which is very close to a true “deathball” shape. Note the yellow dots representing the sliders he threw this season:

Even without movement on the glove side, this form can still be extremely effective. When Kumar Rocker made his debut, some analysts threw 80 points at his “deathball” slider. Erceg's slider is shaped the same as Rocker's, but Erceg throws his slider a few miles per hour harder.

Erceg's elite speed, move-neutral arsenal, and rapidly improving command ability (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 this post) suggest that I told myself he could make the transition to pitching. Even if he loses two or even three mph while stretching out to six innings, the fastball velocity will still be well above average. And if the royals actually choose this route, they could reap significant benefits without risking too much. According to Roster Resource, they have him under team control for the remainder of the 2020s, giving them plenty of opportunity to reverse course if things don't work out.

Lucas Erceg, first-class major league starter – that would be the end of 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 switched to pitching. Just 18 months ago, our lead prospect analyst Eric Longenhagen wrote that “his mechanical inconsistency is impacting his fastball position,” but noted that Erceg “has a chance to make a lasting impact in the big leagues if it works with him.” “Command-wise, it works.” He's still so new to this area so it's easy to imagine what could be.

But that's all in the future. Right here, right now, in the middle of the playoffs, Erceg is the primary weapon of a surprisingly solid Kansas City bullpen. And in my opinion it is the change that sets him apart.