Zac Gallen Pitched Beyond his Numbers in 2023

Right-hander Zac Gallen solidified himself as the Diamondbacks' ace in 2022 with a career-best in ERA (2.54), innings pitched (184.0), WHIP (0.91) and batting average against (.186). He set the Diamondbacks record for most consecutive scoreless innings, passing right-hander Brandon Webb with 44 1/3 innings. 2022 was, in every sense of the word, a dominant year for Gallen.

With a year as special as 2022, fans were excited to see what the 2023 season had in store for the newly-crowned ace of the D-backs rotation. Gallen's season was certainly still an ace showing, but fell a bit short of expectations as the season waned.

After a rough couple of starts to open the season, Gallen settled back in to his former dominant self. Following a four-run outing against the San Diego Padres, Gallen went on to allow zero runs for the rest of the month of April. He struck out 41 batters over that stretch, walking just one batter as he began a new scoreless innings streak. This streak would end at 28, but not before the right-hander lowered his ERA to 2.15 and WHIP to 0.77. 

Gallen pitched well through May, but hit a bump as he was touched up for eight runs over the course of 3 2/3 innings against the Pittsburgh Pirates. Gallen's summer was still by all measurements a solid one, but not quite up to the lofty standard the ace had set for himself, as he allowed one home run in each of his June starts, recorded a season-low 26 strikeouts for the month and pitched to a 3.69 ERA over five starts.

Despite the slight dip in his numbers, Gallen was awarded the honor of starting the 2023 All-Star game, where he pitched a scoreless inning, allowing one hit and delivering a huge strikeout of two-way superstar Shohei Ohtani. 

Gallen's numbers continued to dip following the midsummer classic. The long ball began to develop as more of an issue, as Gallen allowed seven home runs in five starts, allowing multiple in three of those games. His monthly ERA sat at 4.45, and although his WHIP was still a respectable 1.02, and opponents were only hitting him at a .225 rate, he was getting hit hard and early. 

August saw the ace improve. He pitched a Quality Start in five straight starts, before falling victim to a five-run start against the National League West juggernaut Dodgers. As Arizona's playoff push began in September, it looked like Gallen was struggling in most of his starts.

However, on September 8th, in a crucial start against the Chicago Cubs (who were hot on the D-backs' heels for a Wild Card spot), Gallen delivered his biggest start of the regular season. The ace pitched his first career complete-game shutout, going nine full innings, allowing only three hits and zero runs, while striking out nine batters. He was able to finish the contest with only 107 pitches, and the D-backs took a razor-thin 1-0 victory.

Gallen continued to rack up the strikeouts, ending his regular season with 220 but also continued to get hit at a rising rate, as his once sub-3.00 ERA had ballooned up to a still respectable 3.47. 

Gallen's playoff numbers don't jump off the page either. His postseason ERA sat at a pedestrian 5.27 through his first five starts, with a 1.50 WHIP and 18/13 K/BB. These weren't the type of outings D-backs fans had been used to seeing out of the ace, but he still accounted for some memorable moments, including two gritty back-to-back starts against the Milwaukee Brewers and Los Angeles Dodgers. In Game Two of the Wild Card, Gallen allowed two first inning runs, before settling in and pitching a five-inning shutout to help secure the sweep with a 5-2 victory in Milwaukee.

Game Two of the National League Divisional series saw Gallen get into a jam. With runners at the corners, and a 3-1 lead, Gallen faced Dodgers MVP nominee first-baseman Freddie Freeman. On a 3-2 count, Gallen dropped a devastating knuckle-curve into the heart of the zone, ending the Dodgers' hopes for a rally and helping send the D-backs on their way to a 4-2 victory at Dodger Stadium.

With the D-backs facing elimination from the World Series, Gallen put together his best playoff start when it mattered most. The 28-year old right-hander took a no-hitter into the seventh inning, becoming the first pitcher in history to do so facing elimination, en route to a 6 1/3 inning, 1 earned run performance. Unfortunately, it was not enough, as the D-backs were shut out by the Rangers, but Gallen's performance was one to remember.

Gallen certainly showed flashes of the dominant ace D-backs fans know him as, but a puzzling aspect of his 2023 campaign came from the disparity between his home and away starts. At Chase Field, Gallen put forward a 2.47 ERA, with an incredible 120/18 K/BB and just seven allowed home runs. 

Away games posed a challenge to the right-hander, however, as his ERA skyrocketed to 4.42 outside of Arizona. He more than doubled his home run number (15), allowed a slugging percentage nearly 80 points higher (.422 to .339) and his K/BB decreased to a 100/29. 

However, his less-than-expected numbers at times don't do justice to the pitcher Gallen really is. Even in a (somewhat) down year, his pitching run value ranked in the 97th percentile (25). His FIP (3.26) was nearly 20 points better than his ERA, and his K/9 (9.4) and HR/9 (0.9) both ranked well above average. Even when it looked like Gallen was walking more batters in 2023, he ranked in the 88th percentile in walk rate.

Arizona's thin starting rotation would not have gone nearly as far without Zac Gallen anchoring down the #1 role. The D-backs do not go on their World Series run without his efforts. The ace provided an above-average 3.0 WPA (Win Probability Added), helping the D-backs in many crucial moments even in some of his rougher starts.

The D-backs' ace still finished with a respectable 3.47 ERA, a career-best 17-9 record, and placed third in the Cy Young Award voting, behind Padres left-hander Blake Snell and Giants right-hander Logan Webb. Gallen tied right-hander Zack Greinke and left-handed legend Randy Johnson for the ninth-most wins in a season by a Diamondback, with the most pitcher wins for Arizona since Greinke's 17-win season in 2017.

One thing to note: Gallen eclipsed his previous season-high in innings pitched by almost four full starts. As he began to reach his 210-inning total (243 2/3 including playoffs), his control began to dip, and he began to get hit harder. It's possible that fatigue played a role in his lackluster end to the 2023 season.

2024 Status and Outlook

While Gallen's relative letdown in the ERA department might have led to some discussions regarding Merrill Kelly's status as the ace of the squad, Gallen will most certainly retain the #1 starter role going into 2024. While Steamer projects a slightly worse ERA for Gallen in 2024 (3.83), it seems more likely that the ace will find a way to even himself back out closer to the dominance seen in 2022 than continuing his struggling trajectory, especially with a more solidified starting rotation and bullpen to take some of the pressure off the right-hander. It wouldn't be foolish to expect another year of wins, Quality Starts and strikeouts from the Milkman in 2024