How D-backs' Minor League Signing Became Hidden Gem

Despite how it ended, this signing was a win for the Diamondbacks.

Jun 30, 2025; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Shelby Miller (18) throws in the ninth inning against the San Francisco Giants at Chase Field. Mandatory Credit: Matt Kartozian-Imagn Images | Matt Kartozian-Imagn Images

The Arizona Diamondbacks went through one of the more unpredictable seasons in recent history in 2025.

Many players who were expected to lead the charge either underperformed or went down with significant injury. In turn, that led to some surprise players rising to the occasion and contributing at a higher level than expected.

One such example was right-hander Shelby Miller, who made his return to Arizona on a minor league deal ahead of Spring Training. And yet, by mid-season, Miller was the Diamondbacks' closer — a move made out of necessity, but not without merit.

As Arizona Diamondbacks On SI continues to break down the individual seasons of every player that contributed to the 2025 D-backs roster, the below article will be updated with the proper links to every season review as they are published.

Related Content: Breaking Down Every Diamondbacks Player's 2025 Season

Arizona Diamondbacks 2025 Player Review: Shelby Miller

Shelby Miller 2025 and career stats | Alex D'Agostino

Miller had been in the midst of a career resurgence, excelling in a relief role with the Dodgers and Tigers in 2023 and 2024. The D-backs took a minor league flier on their former starting pitcher, and he firmly earned a role on the major league club coming out of Spring Training.

Miller quickly became one of Arizona's more reliable relief options, allowing zero earned runs in his first month of action. He even managed to pick up five saves in the month of May.

When Justin Martinez went down with an injury in June — the second D-backs closer option to suffer that fate — Miller took over that role, going 5-for-7 in save opportunities while maintaining a sparkling ERA, which never ballooned beyond 2.18 as a member of the Diamondbacks.

And then, as so many other Arizona hurlers did in 2025, Miller went down with an forearm strain. It was not season-ending, but it would end his time with the D-backs. While still on the IL, Arizona traded Miller at the Deadline to Milwaukee alongside fellow injured pitcher Jordan Montgomery for just over $1 million in salary relief.

At the time, it was a puzzling decision. But Miller would go on to struggle as a member of the Brewers, giving up six runs in 9.2 innings. On September 1, he felt a pop in his elbow, which would ultimately lead to Tommy John Surgery.

Shelby Miller: 2026 Outlook

Miller likely won't be able to pitch at all in 2026 due to the surgery. It was an unfortunate turn for a veteran arm who had begun to turn his career around at a late stage. The 35-year-old will most likely be out until 2027 — his age-36 season.