Extension candidates for the Arizona Diamondbacks to consider

Pitchers

Zac Gallen would be at the top of my list. Gallen has now finished in the top five in Cy Young voting two years in a row. He has pitched 394 innings in the last two years, the 8th most in baseball, working to a 3.04 ERA, 3.16 FIP, and 1.02 WHIP. Gallen strikes out a healthy amount of batters with a 26.9% K-rate but has an even more impressive 6% walk rate. Home runs haven’t been much of an issue either as the right-hander has had a 0.85 HR/9 rate since the outset of the 2022 campaign.

Gallen is heading into his age-28 campaign but is in his next to last year of control. 2025 marks his final year of arbitration before he heads into free agency. His first free-agent season will be his age-30 campaign. If Gallen reaches free agency, his contract might look something like Carlos Rodon. Rodon also signed a long-term six-year/$162 million deal with the NY Yankees prior to his age-30 season. Rodon had +10.5 bWAR in his two years prior to heading into free agency. Gallen has +9.6 bWAR in the last two seasons. If the D-Backs start negotiating before he hits FA, they might get him for something closer to $150 million.

Merrill Kelly is another large rotation cog that is soon to hit free agency after the 2025 season. The D-Backs hold a club option for 2025 worth $7 million, and so long as nothing catastrophic happens to Kelly in 2025, it will assuredly get picked up. Kelly has also been extremely effective the last two seasons with a 3.34 ERA, 3.85 FIP, and 1.16 WHIP over his last 378 frames. He has a respectable 23.8% K-rate, 8.5% walk rate, and 0.98 HR/9. He has posted back-to-back +3.0 bWAR and fWAR seasons.

Kelly is older than Gallen, as his first year after signing a new contract will be his age-36 campaign. However, he’ll definitely land a deal if he's still effective. At that age, he might have to settle for a one-year guarantee, but with the rest of the years being option/buyout seasons. I could see a one-year deal with the second and third years as team options.

Extending Brandon Pfaadt now might be a good idea. The right-handed headed into August with an 8.20 ERA, 7.22 FIP, and 1.63 WHIP. The only good thing to say about his first handful of outings was his 6.4% walk rate. Pfaadt had struck out just 17.5% of the batters he faced, with a HR/9 rate over 3.00 at 3.13. However, from that point forward, Pfaadt had a 4.14 ERA, 3.89 FIP, and 1.26 WHIP. He lowered his BB% to 6% while upping his K% to 25.6%. His HR/9 also returned to Earth, settling at 1.38. Pfaadt then pitched extremely well into the playoffs.

It would be a good idea to try and take advantage of Pfaadt’s so-so rookie season. Signing him to a low-cost extension would be great. But like I said with Moreno, Pfaadt might not be willing to negotiate an extension right now for the same reasons. But Pfaadt and Gallen could be a very good and homegrown 1-2 punch for the Diamondbacks for years to come if they extended both players.

As of right now, the only relievers that would be worth considering signing to extensions are Paul Sewald and Kevin Ginkel. Sewald is a free agent after this season. He’s been a quality closing pitcher now for the last three years. Ginkel had an outstanding 2023 breakout campaign and became the go-to set-up man for the Diamondbacks. He is under control via arbitration for three more seasons.