Top Diamondbacks Prospects Off to Hot Starts in 2025 Minor League Season

The minor league season has been in full swing for three weeks, four for Triple-A players. At this point, we're seeing a larger sample of how the Arizona Diamondbacks' top prospects are performing. These six prospects have gotten off to strong starts to begin 2025.

Kristian Robinson (No. 38)

Kristian Robinson is off to a pretty decent start with Amarillo. In his first 20 games, he's hitting .268 with five home runs and a 1.001 OPS. FanGraphs rates his offense to be roughly 49% better than the league average player with a 149 wRC+.

Robinson still has a prohibitively high strikeout rate, with a 30.8% rate in 91 plate appearances. At the same time, he's walking at a 16.5% rate so he's not a free-swinger. Another encouraging sign is that his overall swinging strike rate is down from 16.0% in 2024 to 12.7% in 2025 per FanGraphs. That means his overall contact rate has improved, which is an important development for a hitter who boasts the raw power he has.

Another encouraging development has been a change in the batted ball type contact. Robinson's ground ball rate is down nearly 12% from 49.5% to 37.8%. With the type of bat speed he possesses, clocked as high as 83.0 MPH in the Arizona Fall League, hitting the ball in the air more often will allow him to better utilize his one plus offensive tool.

Due to concerns about contact, Robinson still profiles as a fourth outfielder type that serves as a great complement to the outfielders currently on the major league roster.

Kyle Amendt (No. 25)

As mentioned in the minor league recap for Sunday, Amendt has not allowed an earned run in 10 appearances. The right-hander holds a career 1.89 ERA in the minor leagues, quickly ascending up the organization's ladder since they made him a ninth round selection in the 2023 MLB Draft.

Behind his 0.00 ERA is a pretty solid strikeout-to-walk ratio of 13/4. He's punching out hitters at a strong 27.7% rate and a solid 8.5% walk rate. He's making the case to be a midseason call-up candidate for the bullpen, which is still in scramble mode after losing A.J. Puk to injury and Justin Martinez's recent health concerns.

Amendt attacks the strike zone with a vertical approach, using an over-the-top delivery. His high-ride, low-90s fastball and upper-70s curveball have purely vertical shapes as a result of his delivery.

Mason Marriott (NR)

Marriott isn't as highly touted as some of his peers from the 2024 draft class, but he's off to a terrific start with High-A Hillsboro. The right-hander is 1-0 with a 2.29 ERA in four starts. Opponents are batting .188 against him and have struck out in 32.5% of their plate appearances.

The only concern with Marriott is a slightly high walk rate of 10.4%, so that will be something to watch as he gets more starts. Last time out, he completed six scoreless innings with six strikeouts.

Last year, Baseball America published a scouting report on the Diamondbacks' sixth rounder. His fastball sits in the 92-95 MPH range with a curveball, slider, and changeup. The report notes that Marriott's arsenal is a bit shallow, needing to add velocity and/or develop his slider to stay viable as a starting pitcher prospect.

It will be interesting to see what changes he's made to his approach and individual pitches in 2025. Otherwise, he projects as a middle reliever who can rely on a fastball/curveball combination.

Hayden Durke (NR)

Durke is a lottery ticket prospect with a huge payoff of a backend reliever if his development continues to go well. He has the stuff to overpower hitters, sitting 95-98 MPH with a four-seamer and two quality breaking balls between his curveball and slider.

In the early part of the season, hitters in the Northwest League have been overpowered by the 6'1" right-hander. He's currently sporting a strikeout rate of 48.6% in seven appearances with Hillsboro and a swinging strike rate of 18.4%. When batters have made contact, they've put the ball on the ground 63.6% of the time.

Another area Durke has shown significant improvement in is jumping ahead of hitters with Strike 1. His first-pitch strike rate has improved to a career-best 51.4%. With the overpowering stuff he has, that's more than half the battle, as was the case with Justin Martinez when he came up the system. Improved strike-throwing ability will be the key for him to get to the major leagues.

Slade Caldwell (No. 2)

The Diamondbacks' top selection of the 2024 draft has gotten off to a solid start. In his first 18 games, Caldwell is slashing .310/.524/.517 with a home run. Overall, his offensive contributions add up to a 188 wRC+, the highest among the organization's top prospects.

Caldwell has a walk rate of 23.8% and a strikeout rate of 29.8%. Both rates point to a very selective hitter at the plate. He's watched 25.4% of the pitches go past him for called strikes and has only swung at 27.3%. There isn't a lot of swing-and-miss in his game, with just a 5.8% swinging strike rate, so that strikeout rate should go down when he has a better handle on which pitches he can drive.

It's a strategy that can work in the lower minors, where many pitchers struggle to throw strikes, although there's always a fine line between being selective vs. being passive at the plate. That often will be the separating point, especially when he climbs to a level where pitchers are more aggressive in the strike zone.

Ryan Waldschmidt (No. 4)

If Slade Caldwell has been the most productive hitter in the Diamondbacks' system in terms of wRC+, then Waldschmidt is second at 185. The second of three first round selections in 2024 is also off to a hot start in his first full year in the organization. He's currently slashing .318/.483/.561 with four home runs, 16 RBI, and 18 runs scored.

Like with Caldwell, there is a high strikeout and walk rate in his profile. Waldschmidt has been very selective, swinging at just 34.9% of the pitches he's seen. While his strikeout rate is above 20%, his swinging strike rate sits at just 7.0%.