Sal Stewart Is Adjusting

55 percent. That's the rate at which Sal Stewart chased four-seam fastballs thrown outside the zone in the first two weeks of May — more than half the time a pitcher threw a heater where it didn't need to be, our guy was swinging at it. For a hitter who walked at an 18 percent clip in April and posted a wRC+ of 185, that number doesn't belong to him. The number I'm looking at now is 18 percent.

May has been a strange month. The surface results look fine, he's still hitting, still getting on base, but the pitch data tells a story about a 22-year-old getting his first extended look from a league that has figured out a plan. The plan is Zone 14. That's the Savant designation for low-and-away to a right-handed hitter, and pitchers attacked it on 22.6 percent of pitches thrown to Stewart in the first two weeks of May, the highest of any single zone in the park. Add in the elevated four-seamer above the zone and you have a two-part script: pound the away corner low, sneak the heater up and out when he starts hunting the low pitch.

Stewart's swing is almost designed to be late on velocity. Jay Jaffe's spring writeup described it perfectly, noting that he "tends to be late on fastballs and is rarely on time to pull them in the air." Most scouts hate "inside-out" prospects who do this because they think it limits the power and is a sign they're overmatched by fastballs. So on the surface, being late and hitting to the opposite field should be a liability for Sal. But it isn't.

The key to Sal's swing is that it's optimized for a very specific and effective contact point. When he makes contact with the ball, the barrel of his bat arrives in strong position with his hands inside the ball. This leads to him extending and hitting the ball deeper in the zone than a pull hitter. This results in him looking "late" by conventional standart, but it's actually his optimal timing. His 21.3 percent barrel rate and 105-plus mph EV90 are happening off pitches he's driving to right-center, not balls he's pulling down the third base line.

Thers is a drawback to this, though. When he's chasing an fastball out of the zone too far in or outside, he tends to actually late on a pitch he can't direct. This leads to weak contact and whiffs. The key to avoid this is having a great understanding of the zone, which is on display when he's hot and missing when he'd not.

For the first 13 games of May, the league seemed to have figured this out. I pulled the pitch data expecting to see pitchers using sliders or breaking balls to beat him (which is usually what happens to hot young pitchers ie Rece Hinds and Aristides Aquino). Instead, what I got was confirmation that he was experiencing a chase-rate problem.

His overall chase rate was 33.6 percent, which was about two points higher than his April rate. He was also swinging at just over half of his pitches, which is a sign that he was pressing. The contact he made averaged 82.5 mph in exit velocity, soft for a hitter capable of 105-plus, and his xwOBA on batted balls was .401. That .401 is a fine number for most hitters, but it was relatively bad for him.

Then something shifted around May 15.

I don't know whether it was a film session, a coaching conversation, or just a 22-year-old feeling the pattern and correcting it. What I do know is that the last five games look like a different hitter in the Statcast data. And the box score is starting to reflect it: the 4-for-5 game he had this morning (May 20th vs the Phillies) with three RBIs and a home run suggests Sal's adjusting to how pitchers are approaching him. This is terrific, because that's the key to long-term success in the show.

Let's take a look at his pre-May 15 numbers and after. On four-seam fastballs out-of-zone (OOZ), his chase rate before the 15th was 55 percent. Since then, it's dropped to 18 percent. His overall swing rate dropped nine points, from 54.8 to 45.7 percent, and his chase rate fell from 33.6 to 17.9 (that's nearly half).

He's also laying off junk pitches, too. His chase on changeups fell from 29 to 12 percent, and his chase on out-of-zone sinkers went from 31 percent to zero. Yes, it's only been 6 games, but the direction holds across every pitch type he'd been fishing for during the first part of the month.

And when he does offer on the away pitch now, his contact pointed in the right direction. His xwOBA on pitches in the away half of the zone over the last five games is .372, so it's not like he's conceded that part of the plate to pitchers. In fact, I think he's reclaimed it.

There are areas for improvement. He's actually whiffing on low pitches, which wasn't a problem two weeks ago. I'm guessing that like velociraptors testing the fence in Jurassic Park, pitchers are probing for a new way to beat him. The low sweeper, the curveball bouncing in the dirt, the two-strike sinker below the knees seem to be what they'll try next. I wouldn't build a case on 34 pitches. But it's there, and it's the logical next step if pitchers decide that the high-and-away attack isn't working.

The specific pitch to watch going forward is the slider. It's the one type that's been actively costing him all season, running -0.94 run value per 100 pitches. Pitchers know this, which is why he sees the slider 32 percent of the time, more than any other offering. As pitching staffs sit down with their advance scouts and lean on that knowledge, I'm watching the OOZ chase rate. If it stays below 25 percent over the next month, the adjustment is holding. If it climbs back toward 40, it hasn't.

Note: The pitch data above runs through May 19. This piece was finished the day after Stewart went 4 for 5 against the Phillies on May 20 — 3 runs, 2 RBIs, a home run on a cutter waist-high on the inner edge of the zone. An inner-half cutter at the belt is exactly the pitch you attack when you stop expanding on pitches away.