This article is part of a series counting down the Diamondbacks Top 30 prospects entering the 2024 season. These rankings are determined by Michael McDermott, in conjunction with the Inside the Diamondbacks staff.
Summary: Justin Martinez was originally signed as an outfielder in March 2018, but quickly moved to the mound when he could reach upper 90s velocity. Once looking like a breakout prospect entering the 2021 season due to his premium velocity, he suffered a series of injuries after seven starts with Visalia and ultimately underwent Tommy John surgery. He returned to the mound in 2022 and put up solid numbers at three different levels of the minors and the Arizona Fall League. The D-backs added him to their 40-man roster the following winter. With a fastball that averages 101 MPH and two potentially plus secondary offerings, Martinez has the ceiling of a future closer once he gets his sights locked in to the strike zone. With only 31 days of service time on his record, he is still rookie eligible in 2024.
Rank: 23
Age: 22
Height/Weight: 6'3" 180 lbs.
Throws: Right
Tools: Fastball 70, Slider 55, Splitter 70, Command 30, Overall 40
ETA: 2024
What the D-backs are saying about him?
"When you're gifted with an arm like Martinez has been gifted with, it's almost like you have a race car that is a little too fast and you can't control the darn thing. The horsepower is so high....my dream is to drive a Porsche. I never have, but I'm sure if I stepped on the accelerator it would shock me a little bit as to how fast it would go because I'm used to Kias. I think that's the case with Martinez, he just needs to kind of wraps his arms around 'what I have and how it should feel' and things like that. He's going to be special down the road." - Pitching coach Brent Strom
2023 Recap: After getting added to the 40-man roster, Martinez was optioned to Triple-A to open the 2023 season. After pitching to a 3.77 ERA in 28 games with Reno, the D-backs called him up. Martinez debuted against the Pittsburgh Pirates, recording his first career strikeout but allowing two runs. For the rest of the year, he was an up-and-down arm as the inability to consistently land strikes kept him from establishing himself in the bullpen. In his first 10 appearances, he struck out 14 but also walked 11 over 10 innings. Despite finishing the regular season on the big league roster, he was never in consideration for a postseason roster spot.
There were some positive moments, in particular a series against the Padres in mid-August where he flashed that closer potential. With an exhausted bullpen following a series at Coors Field, Martinez recorded a four-out save with three strikeouts in San Diego. Two days later he effectively closed the door on the Padres season, recording the final five outs in a blowout win.
2024 Expectations: Martinez is far from a finished product, but will continue to get opportunities due to his stuff. He has two options remaining on his contract, so the organization is willing to be patient for him to continue working on throwing strikes more consistently. With the velocity and movement of his secondaries, pinpoint command isn't necessarily a requirement for success as opposing to just filling up the zone. The key will be watching his walk rate in both Triple-A and MLB. If he can get his walks per nine to under 5.0, he'll be able to establish himself as a big league reliever. The more strikes he throws, the more likely he'll reach his ceiling of a backend arm.
Projection: At the current stage of his development, Martinez is an up-and-down arm. However regardless of what role or inning he ultimately is tasked for, the projection is a reliever who's getting no more than six outs. He'll never necessarily develop strong command, so his future will be determined by how aggressively he uses his stuff in the strike zone. Right now he looks the profile of a middle guy who may develop into a backend arm or even the team's closer down the road.
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