Spencer Strider's fastball is behaving differently

It's not just the velocity, but also the movement profile that's different post-surgery

(Bit of a shorter newsletter today after my hectic weekend of college baseball press boxes and rain delays. We’re back to normal starting tomorrow with both the morning deep dive and the game stories after every single matchup.)

Spencer Strider had arguably the best start of his 2025 season on Sunday afternoon in San Francisco’s Oracle Park, allowing just three hits and three earned runs in six innings.

He still lost, though, after consecutive walks in the fourth inning. Both came around to score, and the man who drove them in, Mike Yastrzemski, scored the go-ahead run on a defensive error.

Yes, Strider’s fastball velocity still isn’t back to its normal 2023 levels of 97.2 mph on average, sitting just 94.8 and maxing out at 96.5 in this one. But something else about the fastball caught my eye: Its horizontal movement.

Strider’s always had the platonic ideal of a “backspinning” four-seam fastball - by getting behind the ball and having almost perfect seam orientation, virtually all of the spin that Strider’s imparting to the ball with his fingers translates into the pitch’s movement in the way that he wants. This concept, called “active spin percentage”, has generally hovered around 97-9% and allows Spencer’s four-seam fastball to be one of the best in the league.

Or rather, allowed.

After the injury, it’s no longer coming in at 97.2 mph with a 99% active spin percentage and an elite 18.4 inches of induced vertical break, a trio of traits that are literally unmatched across the sport and allowed it to be one of the best heaters in MLB.

Instead, it’s coming in at 95.2 mph with 96% spin and 17.6 inches of induced vertical break. It’s also moving more horizontally than ever before.

Let’s talk about why.

A similar problem to Sale

Just like Chris Sale dealt with earlier this season, Strider’s arm angle is different, having dropped a full seven percent. Instead of his typical 48°, it’s all the way down to 41°.

And that’s caused a few changes.

The first is more horizontal movement.¹ Instead of its normal six inches of horizontal movement, Strider’s fastball is getting eight and a half. Seems good, right? Moving the ball 2.5 inches farther horizontally means it goes from the barrel to the thin part of the bat, right?

Not exactly.

Because it only moves to the correct spot if he knows where it’s going to go and adjusts his target accordingly. Plus, any movement laterally, by nature, isn’t movement that’s contributing to the induced vertical break that keeps the ball elevated in the top of the zone and over a batter’s swing.

The good news is that Strider’s fastball isn’t in the dead center of the zone as much this year. He ran a 6% rate in 2023, allowing a .345 average and .440 wOBA on the pitch, but he was at just 4.034% entering Sunday’s start.

(The lower velo and different movement profile IS allowing it to get hit hard when he throws it in attack zone 5, though, to the tune of a .667 average and 1.052 wOBA.)

We could really see that on Sunday, with several of Strider’s walks coming on fastballs thrown to the outside edge of the zone. He appeared to make a concentrated effort to keep the fastball on the black versus the power hitters, although he didn’t always succeed.

In the past, by contrast, he generally aimed for the heart of the plate with the heater, knowing that the relative lack of horizontal movement would keep the pitch somewhere over the plate and allow him to attack hitters without excessive walks.

But a consequence of this move from the heart of the zone to the edges is that his walks are up.² And I guess, within reason, that’s a trade-off you’d be willing to make, because no contact is better than hard contact.³ It’s worth pointing out that this trade-off is working - Strider allowed only three hard-hit balls on Sunday and no barrels, although all three hard-hit balls were over 100 mph and fell for hits.

SIDEBAR: I wonder if the lower arm slot is intentional. A recent study seems to suggest that a lower arm slot can measurably reduce joint stress, at both the elbow and the shoulder, without meaningfully lowering velocity. Pitchers who have cited this for their arm slot drops this season include Paul Skenes and Jacob DeGrom.

Here’s a great video from my guy

Lance Brozdowski

about arm slots from last month:

Strider’s still not sequencing enough

In that Giants outing, his first quality start since returning from elbow surgery, Strider threw almost exclusively fastballs and sliders. He used each of the curveball and changeup exactly once, both landing outside the zone and not eliciting a swing from that batter.

We talked about this, too - Against the Nationals, he went 13% changeup and 9% curveball, but was back to his old ways on Sunday. Some of that may be gameplanning - of the ten best combinations of one specific hitter on one specific pitch for San Francisco’s roster, three of them are a slugger against a changeup. From a Run Value per 100 pitches (RV/100) perspective, no single hitter/pitch combination is worse to throw when facing this team than throwing a changeup to Mike Yastrzemski, who sports a 5.4 RV/100.

But Strider overall needs to be more aggressive at throwing more of his pitches more often. It’s an easy adjustment to make, especially after he’s already fixed the locations on his fastballs to be more on the periphery of the zone versus the heart.

While I still don’t know how long until the velo comes back, he’s doing everything else he needs to do to be an effective, albeit not dominant, major league starter again.

1. That’s not surprising at all, by the way. Moving the arm angle down always results in more lateral movement.

2. Quantifying this: 2.8 BB/9 in 2023, 3.96 BB/9 right now.

3. Blake Snell’s built a two-time Cy Young-winning career off of the idea of ‘I’d rather walk you than give you anything you can hit hard.’