Kade Anderson’s first major league start gave the Mariners a look at the kind of arm that made him one of the game’s top prospects. It also offered another reminder that the baseball itself can change the way a pitcher’s fastball plays.
The 22-year-old left-hander worked 5.2 innings in his MLB debut over the weekend, allowing three earned runs on five hits, including two home runs, and two walks. He struck out five on 81 pitches and finished with a no-decision.
What stood out beyond the line score was the shift in Anderson’s fastball from Double-A Arkansas to Seattle. In the minors, his four-seamer averaged 93.6 mph and topped out at 96.6, with 16.8 inches of induced vertical break, minus-8.3 inches of horizontal break, 2,211 rpm of spin and 6.53 feet of extension. In the majors, the velocity held at 93.6 mph on average, but the pitch maxed at 95.5, the IVB dropped to 15.4, the horizontal break moved to minus-7.3, spin fell to 1,976 rpm and extension ticked up to 6.9 feet.
That kind of change is exactly why the difference between the MLB ball and the minor league ball matters. Professional baseball uses two different baseballs: the MLB ball in the majors and Triple-A, and a separate minor league ball everywhere from Double-A down.
They match in size and weight, but not in construction. The major league ball is hand sewn in Costa Rica with aniline-tanned leather, giving it a darker, smoother surface and wider, flatter seams.
The minor league ball is made in China, uses a varied quality of hides, and is machine-built with higher, more pronounced laces.
Those details can alter pitch movement, especially on fastballs. Statcast’s induced vertical break measures how much a pitch would move up or down in a zero-gravity environment, and it’s one of the key numbers for understanding fastball shape. The change from a minor league ball to an MLB ball can affect that shape directly.
Anderson’s profile makes him one of the pitchers most likely to feel that effect. Lower-spin fastballs with higher spin efficiency tend to be the most sensitive to a drop in raw spin, and Anderson fits that description. In his first MLB outing, he produced less raw spin, which likely meant less ride on the fastball.
The trend has shown up before with other pitchers making the same jump from Double-A straight to the majors. Over the last two seasons, only one pitcher lost more induced vertical break on that move than Anderson: Dodgers right-hander Emmet Sheehan.
In 2023, Sheehan’s Double-A four-seamer averaged 96.8 mph with 18.8 IVB, 12.1 horizontal break, 2,483 rpm of spin and 6.44 feet of extension. In the majors, that became 95.4 mph, 15.6 IVB, 11.1 horizontal break, 2,291 rpm of spin and 6.7 feet of extension.
That was a three-inch drop in IVB, more than double Anderson’s decline.
Sheehan’s case also shows that a rocky first look with the MLB ball does not have to be permanent. He later recovered both spin and ride on his fastball in 2025 and 2026. The caveat there is that Sheehan had Tommy John surgery before the 2024 season, so his elbow health at the time of his debut was unknown.
Not every pitcher sees a meaningful change, though. Phillies right-hander Alex McFarlane, called up directly from Double-A in 2026, barely saw his fastball shape budge.
His Double-A four-seamer averaged 98.2 mph with 14.1 IVB, 10.6 horizontal break, 2,579 rpm and 6.29 feet of extension. In the majors, it sat at 100.3 mph, with 14 IVB, 9.5 horizontal break, 2,586 rpm and 6.4 feet of extension.
Braves right-hander Spencer Schwellenbach had a similar experience when he reached the majors in 2024. His Double-A four-seamer averaged 95.1 mph with 13.5 IVB, 6 inches of horizontal break, 2,391 rpm and 6.61 feet of extension. In the majors, it moved to 96.1 mph, 13.4 IVB, 5.7 horizontal break, 2,265 rpm and 6.7 feet of extension.
McFarlane and Schwellenbach both throw lower-spin-efficiency fastballs, though McFarlane gets above-average raw spin and Schwellenbach does not. Even so, that lower efficiency has not meaningfully altered the way their fastballs move.
The larger takeaway is simple: the minor league ball can shape a pitcher’s early career in ways that matter, and Anderson is now another example of a young arm adjusting to that change. Like Sheehan, he appears likely to make those corrections and regain some of the lost vertical break and raw spin by 2027.
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