The Diamondbacks still have one remaining need left to address, a late-inning bullpen arm. So far they have not been linked to many names, and have been more aggressive in the trade market than free agency.
The cost to land Robertson is mostly money, as it will take at least $10 million. There is a lot of mileage on his arm, as the 39-year-old has made 861 career appearances. In 2024, he was electric for the Texas Rangers. In 68 appearances, he pitched to a 3.00 ERA and 99 strikeouts in 72 innings.
In 2024, Robertson relied on his signature cutter and knuckle curve combination. The two pitches accounted for 90% of his pitches. The cutter averaged 93.3 MPH and opponents hit .163 against it. It yielded a whiff rate better than 30% and was his best putaway pitch. The knuckle curve got hit hard, with a .274 opposing average against and batted ball metrics suggesting the results should have been worse..
Pitching in Arizona isn't easy, as elevation and dry air are factors that negatively affect stuff. Robertson still showcased electric stuff with the Rangers in 2024 but even a small change could spell disaster if the location isn't good. Unlike Melancon, the Statcast percentiles were mostly in the red instead of the blue in his walk year. His fastball run value clocked in at +19 for the season although the breaking stuff was -7.
The downside has been the team's track record at acquiring veteran closers. While Fernando Rodney can be considered a success, they've flopped on Brad Boxberger, Greg Holland, and Mark Melancon. Should Robertson follow this pattern, the team is in bad shape with their bullpen for 2025.
Unless they have any alternative options in the works, then Robertson would make sense on a one-year deal. That gives them upside without too much downside and would allow Justin Martinez to grow into the closer role for 2026.