PHOENIX – For years, Zac Gallen represented everything the Diamondbacks wanted their pitching staff to be. He consistently outsmarted hitters, mixed pitches with precision, and lived one step ahead of every lineup. That formula helped turn him into a Cy Young contender and one of baseball’s most dependable starters. Today, that blueprint is falling apart, and it’s hurting Arizona far more than one bad stat line every fifth day.
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Jun 20, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen (23) reacts after being taken out of the game in the fifth inning against the Minnesota Twins at Chase Field. Mandatory Credit: Rick Scuteri-Imagn Images
The decline appears to be driven by multiple factors working together. Opposing hitters have become increasingly comfortable against Gallen’s sequencing, while the margin for error that once made his arsenal elite has nearly disappeared. His fastball velocity has remained around 93 mph throughout his career, eliminating the easy explanation of declining arm strength. Instead, the deterioration has shown up in the finer details that separate good pitchers from great ones, and that is why Gallen is sitting with a league-worst 6.15 ERA.
MLB Worst ERA pic.twitter.com/fs8TmiuitW
— Thomas Nestico (@TJStats) June 28, 2026
Gallen built his career on exceptional pitch tunneling, using tight differences in movement and spin to make every offering look identical until the final moments. Small reductions in spin rate and movement have made his breaking pitches easier to identify, particularly his knuckle curve, which no longer generates the swing-and-miss numbers it once did. Hitters aren’t chasing. They’re waiting for favorable counts and punishing mistakes. That creates a dangerous cycle. As hitters become more selective, Gallen is forced into predictable situations, making his chess-match approach less effective than it once was.
May 23, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen (23) prepares to throw a pitch against the Colorado Rockies during the first inning at Chase Field. Mandatory Credit: Anna Carrington-Imagn Images
The solution isn’t necessarily finding more velocity; it’s reinvention. Many successful veterans have redesigned their arsenals during the second half of their careers by simplifying their approach, altering pitch shapes, and prioritizing execution over perfect sequencing. Arizona’s coaching staff may need to guide Gallen through that same transition before the problem becomes irreversible. Pitchers often decline in their mid-to-late 30s. What’s alarming is that Gallen’s transformation from Cy Young candidate to replacement-level production has happened before turning 31. If the Diamondbacks hope to remain contenders, fixing these issues must be a priority for them going forward.
Arizona Diamondbacks right-hander Zac Gallen (23) warms up before pitching against the Los Angeles Dodgers at Chase Field in Phoenix, on June 2, 2026. © Joe Rondone/The Republic / USA TODAY NETWORK via Imagn Images
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Reporter Benjamin Bliklen covers the Arizona Diamondbacks, Arizona Cardinals, and Phoenix Suns for Burn City Sports. You can follow him on his X account, @BenBliklen
