The Arizona Diamondbacks spent the final day of the 2026 regular season needing help. Their larger failure was spending too much of the year giving away opportunities to avoid that predicament.

The Diamondbacks finished 86-76 after a 9-4 loss to the San Diego Padres. Their elimination became official during the seventh inning, when the Philadelphia Phillies completed a 7-3 victory over the Tampa Bay Rays. Arizona missed October for the third consecutive season.

Injuries complicated the season, but established players also fell short of reasonable expectations. Zac Gallen, Merrill Kelly, and Ketel Marte deserve the most scrutiny for performances that helped leave the Diamondbacks outside the postseason.

Zac Gallen failed to anchor the rotation

Gallen presents the clearest case because his problems extended beyond missed starts.

The right-hander finished 3-9 with a 6.07 ERA across 105 1/3 innings. He allowed 128 hits and 19 home runs while striking out just 64 batters. For a pitcher expected to help lead the rotation, that combination offered neither run prevention nor much ability to escape trouble through strikeouts.

His regression also followed a disappointing 2025, when he posted a 4.83 ERA. The Diamondbacks needed a rebound. Instead, their former ace became an even greater uncertainty.

Elbow inflammation deserves acknowledgment, and judging his effort through an injury would be unfair. Still, the innings he actually pitched produced damaging results, and he eventually moved to the bullpen.

Gallen's diminished effectiveness weakened a rotation already managing other absences. His place atop this list rests on the gap between his expected responsibility and the quality of his work.

Merrill Kelly supplied innings without enough stability

Kelly's 162 innings had value for an injury-stricken pitching staff. His 4.94 ERA explains why that workload did not provide enough relief.

Across 29 starts, the veteran allowed 28 home runs and issued 70 walks against 113 strikeouts. Those numbers made it difficult to trust him as the stabilizing presence the Diamondbacks needed.

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The walks created unnecessary traffic. The home runs made that traffic especially dangerous. Together, they exposed a veteran starter who too frequently gave opponents opportunities to build big innings.

Kelly also dealt with intercostal nerve irritation, which belongs in any fair assessment. However, his substantial workload makes the season more than a small sample distorted by a brief return from injury.

With that said, the 37-year-old right-hander did help keep Arizona alive with two runs allowed over 5 1/3 innings in his finale.

The Diamondbacks could absorb occasional poor starts. Absorbing a 4.94 ERA over 162 innings from a central rotation piece made their path considerably harder.

Ketel Marte's offensive regression proved costly

Marte hit .249 with 22 home runs and a .748 OPS, a 145-point drop from 2025. His September production offered little relief, as he finished the month with one homer and a .684 OPS.

His reliability also became an issue. The 32-year-old switch hitter failed to report for the August 17 game vs. the Boston Red Sox, prompting the Diamondbacks to place him on the restricted list. He later apologized and returned following an injured-list stint for left knee inflammation. The incident followed another absence after the 2025 All-Star break, when his home was burglarized.

Those circumstances deserve consideration, but the Diamondbacks still needed better communication and stronger production from a franchise cornerstone. Marte’s offensive decline and August no-show added to the challenges of a team fighting for October.