Predicting the Diamondbacks Fifth Starter Decision

While the team has not made any official announcement, the competition for the fifth starter's spot in the rotation appears to be settled.

Feb 19, 2025; Scottsdale, AZ, USA; Arizona Diamondbacks pitcher Brandon Pfaadt (32) poses for a portrait for MLB Media Day at Salt River Fields. Mandatory Credit: Allan Henry-Imagn Images / Allan Henry-Imagn Images

The Arizona Diamondbacks have held their cards close to their chests regarding multiple decisions this spring. Spring competitions have included fifth starter, backup catcher, utility infielder, as well as the final three spots in the bullpen and closer.

The D-backs have not made any of their decisions public, assuming they have actually made them. All roster decisions are made by Mike Hazen's baseball operations department, with input from the manager and coaching staff of course.

Five days ago on March 13 I predicted that Jose Herrera would capture the backup catcher role for opening day over Adrian Del Castillo. That prediction appears to be correct as Del Castillo suffered yet another health setback and has not hit well this spring.

Corbin Burnes, Zac Gallen, Merrill Kelly, and Eduardo Rodriguez are locks for the rotation as long as they're healthy. The fifth starter's spot has been a "competition" between Brandon Pfaadt, Ryne Nelson, and Jordan Montgomery.

Today I feel comfortable predicting that Brandon Pfaadt has captured the fifth starter's spot. While the team has probably always been leaning this way to begin with, it's evident that there is no other choice to start the season. It should be emphasized the team has not made any public decision. This is not official. This is my assessment of what they are going to do, however.

Pfaadt looked especially sharp in a recent five-inning outing against the the Padres. Results aside, the sweeper was as good as we've seen it since his very best games of 2024. He is very clearly ready to follow up a season in which he led the team in innings pitched.

I also do not take credit for being especially insightful in this case. In fact the wisdom of the crowds overwhelmingly believed this should be the result. 77.3% of respondents in a poll on X believe that Pfaadt should be the fifth starter. It should be noted this poll went up the morning of March 16, before Pfaadt's outing against the Padres.

Who should be the #Dbacks fifth starter?

— Jack Sommers (@shoewizard59) March 16, 2025

Ryne Nelson was doing his best to keep up with Pfaadt, and prior to Monday, had been doing a good job of that. But he was blown up for nine runs on 11 hits in three innings against the Royals. More importantly, his velocity on his fastball and cutter were both down.

Despite being the team's best starter from July 1 onwards last year, 2025 is a new season. Nelson needed to outpitch Pfaadt by a good margin to capture the fifth spot, and that simply hasn't happened. He will either start the year in the bullpen on Opening Day, or go to Triple-A Reno to remain stretched out as a starter in case someone gets injured.

That's a very important decision, as we discussed with Torey Lovullo yesterday. When a starter is shortened up, it creates injury risk to try to stretch them back out. Bouncing back and forth between starting and relieving results in injury for Jon Duplantier in 2019 and Drey Jameson in 2023.

Related Content: D-backs Lovullo Gives Surprising Answer to Rotation Question

Montgomery entered camp slimmed down 25 pounds, but immediately suffered a strained ligament on his left index finger. That set him back about 10 days or so behind the other starters. When he finally appeared in a game March 8, the stuff on display and results were so bad that he was relegated to a backfield to try to work out his problems.

Montgomery will start again on Wednesday against the Rockies, and we'll see if his velocity and stuff has ticked up. But I believe there is nothing he can do Wednesday to earn that fifth spot. If he is to make the team at all, it will be a long relief, mop-up role out of the bullpen. The Diamondbacks owe him $22.5 million dollars for 2025.

We'll be reporting the team's official decisions as they happen in real time. Stay tuned to Arizona Diamondbacks On SI for all the latest news.