What D-backs fans should expect in Zac Gallen’s debut

Zac Gallen arrives to the Arizona Diamondbacks with some pressure on him.

The D-backs No.1 prospect Jazz Chisholm was traded away for him. The team’s former ace Zack Greinke is now a Houston Astro, which leaves big shoes to fill. Gallen is one of the core pieces of the team’s front office mindset of getting young players who are major-league ready.

But despite being just 23 years old, Gallen has some experience. His seven starts with the Marlins have all been quality outings while he’s been dominating in Triple-A.

How has he done it? And what should be expected of the new starter? Let’s take a look.

Gallen pitched well this season for Miami. In seven starts, he posted a 2.72 ERA with a 154 ERA+. Those are both well above average numbers.

He did it with strikeouts and limiting contact. Gallen had 43 strikeouts in 36.1 innings this season, averaging out to 10.7 strikeouts per nine. Gallen only issued 6.2 hits per nine as well, a number that, if his sample size were much higher, would be in the top ten of the MLB (Justin Verlander allows the fewest hits per nine with 5.4). The lack of contact kept his FIP low at 3.58, while some control issues kept it from being insanely low.

His seven starts saw him issue 18 walks, averaging out to 4.5 per nine innings. But control has never been an issue of Gallen’s, and walks aren’t something that MLB hitters can influence. Command hasn’t been an issue of Gallen’s in the minors; he allowed just 1.7 walks per nine in Triple-A this season, and 3.2 walks per nine last season.

Gallen doesn’t throw that hard. His fastball velocity ranks in the 18th percentile of pitchers this season, per Baseball Savant. Gallen touched 96 MPH in July, throwing a 96.47 MPH fastball according to Brooks Baseball. But his averages sit in the 92-93 range.

He generates high spin rates with the fastball, though, as it ranks in the 73rd percentile of MLB pitchers this season.

Thirteen of Gallen’s 17 walks have come off that fastball, which is really just missing its spot up in the zone. Check out this graph from Baseball Savant:

The numbers represent the percentage of walks that are issued in that area of the zone. As you can see, Gallen is throwing a little too high, or is missing down low.

The walks will figure themselves out, or could simply be an issue of a small sample size.

The high spin rate on the lower-velocity fastball from Gallen works in his favor too, though. While the walks could be a product of putting too much spin on the ball instead of relying on velocity, the pitch could be deceiving batters. Gallen’s struck out 21 batters with the fastball; his changeup ranks second with 10 Ks, followed by the slider with seven. So far, it’s been his bread and butter with two strikes.

He throws the fastball the most. 45.51% of the time, according to Brooks Baseball. That’s followed by his slider 20.39% of the time, and his curve 17.46% of the time. His change factors in 13.87% of the time as well.

It’s a true four-pitch mix Gallen has. And they’re all really tough to hit.