The Right Stuff for Zac Gallen

The Arizona Diamondbacks have a potential future ace in 24-year-old righty Zac Gallen. Making his debut for the Miami Marlins in June 2019, Gallen finished the season with a 1.6 WAR, and armed with a filthy changeup, became one of the more exciting young pitchers to appear in the major leagues last year.

This spring, Gallen will battle for the fifth spot in the Diamondbacks rotation. If he isn’t able to secure a starting role, Arizona may have him begin the season in Triple-A. Gallen could claim that rotation spot with an assist from an adjustment to one pitch, which in turn will tighten up his entire arsenal and help him become one of the tougher pitchers to face in baseball.

Though the sample is limited, Gallen did well during his first 15 big league starts. Through 80 innings pitched, Gallen produced an ERA of 2.81 (3.61 FIP), struck out 96 hitters, and posted a 2.96 K/BB ratio. Gallen also demonstrated good command last year, though his 10.8% walk rate indicated he may have struggled a bit with his control.

Gallen attacked hitters with a four-seam fastball, a knuckle curveball, a changeup, and two types of cutters: a sweeping (or hybrid) cutter and a backspinning cutter. Eric Longenhagen put a 50 FV on Gallen’s overall arsenal, with special consideration given to his changeup (55 FV).

Gallen’s four-seam fastball is thrown with a 12:40 spin direction and around 96% spin efficiency. The lift generated by that high spin efficiency ranked Gallen 31st overall (min 80 IP) in fastball rise and its minimal axis tilt created a decent amount of run. Gallen was consistent with his four-seam usage regardless of where he was in the count and held hitters to a .301 wOBA despite missing bats with it less than he did with his other three pitches. Gallen was a little erratic with its location and left the fastball in the middle zone more than he should have; his spin rate to velocity ratio (25 Bauer Units) suggests the pitch should be kept up in the zone where he was far more successful.

Gallen’s classic knuckle curveball had equal parts sweep (9.1 inches of horizontal movement) and depth (-10.1 inches of vertical movement) under a 7:10 spin direction with 67% spin efficiency. He was a little unlucky with it at times, as evidenced by his .275 wOBA versus his .242 xwOBA. Gallen’s curveball pairs well with his fastball so long as the four-seamer is elevated. When the curve and fastball are used in tandem, the two pitches approach a spin mirror (165-degree axis contrast) but the additional tilt on the curveball breaks it up, going beyond the ideal 170-190 degree contrast.

Gallen’s best pitch last season was his changeup, which produced a 1.69 FIP and a .210 wOBA. Featured more against lefties due to its ability to move out of the reach of their bats, the pitch had a 40.7% whiff per swing rate with a 24.6% K-BB%. The pitch can be described as a fading changeup given the heavy sidespin component coupled with decent depth. Gallen’s changeup sits almost two hours off his four-seamer in terms of spin direction, which is ideal considering that style of changeup works best off a fastball when there’s at least a one hour spread between them. Gallen located his changeup in the zone only 28% of the time last year and induced hitters to chase on over 45% of those put out of the strike zone.

Here’s a look at all three pitches thrown to their ideal locations based upon their design:

That brings us to Gallen’s cutter. His cutter was something of an enigma given that he threw two variants with a spin direction contrast of about 70 minutes between them. Gallen liked to use his cutter more against righties, though it did appear indiscriminately to either handed hitter when he was ahead in the count.

From his debut with the Marlins in June through the end of July, Gallen threw more of a sweeping, hybrid-type cutter that could very easily be categorized as a slider (its nomenclature varies from site to site). Thrown under an average spin direction of 9:40 with heavy gyro spin, its shape created about 7-8 inches of cut with minimal lift. The pitch was then altered after being traded to the Diamondbacks; Gallen adjusted the pitch’s average spin direction to around 10:50 and created more of a back-spinning cutter that doubled its lift but lost very little of its cutting action due to the minor adjustment to its gyro orientation.

The spin comparison on each is demonstrated below using the Driveline EDGE tool:

For a more in-depth perspective on both, here’s an overlay showing the difference between his early (left) and late-season (right) cutters:

Now that we’ve covered the design of both pitches, let’s take a look at how effective each version was last season.

With the exception of a 3% bump in whiffs per swing, Gallen had much better results using the June/July hybrid cutter.

So we see that Gallen’s early cutter was the better pitch, but there are other reasons why it should be deployed in 2020. For one, its design is an ideal fit for his arsenal; Gallen kept the style of his three other pitches essentially the same, which provides a good foundation to base this recommendation on.

The 9:40 spin direction, taking gyro orientation into consideration as well, plays off the spin direction of Gallen’s four-seamer by around 90 degrees. Considering Gallen approaches ideal spin mirroring with his four-seamer and curveball, the hybrid cutter fits in with that pair very nicely. In a vacuum, the three pitches create almost perfect symmetry:

What’s more, the hybrid cutter works well off the changeup, as both of them split in opposite directions with a negligible difference in lift:

Gallen is just 24 years old and there’s a lot of room for growth in his pitching development. Gallen’s coaches note his work ethic as well as the poise he demonstrated in 2019 as signs that he’s headed for a strong season in 2020.

Despite the fact we are looking at a small sample, the hybrid cutter fits Gallen’s arsenal much better than the back-spinner variant. In addition to how it rounds out an effective repertoir, hitters had a harder time dealing with the pitch. Furthermore, Gallen is ahead of the game with how tight his release points are on each pitch, an advantage some pitchers aren’t afforded. Having that additional layer of deception can only improve Gallen’s chances of being a mainstay in the Diamondbacks’ 2020 rotation. With his arsenal tightened up by adjusting his cutter, Gallen could surprise many and end up finishing as one of the better starting pitchers this year.