Ryan Mountcastle could be Diamondbacks ideal trade candidate at first base
With a solid track record and still plenty of upside left to unlock, the Diamondbacks could take a chance on the Orioles first baseman in the trade market.
The Diamondbacks could have a hole opening up at first base, should they lose Christian Walker to another team in free agency. The team lacks ideal internal options, with Pavin Smith as their best candidate in a platoon role. So they may need to turn to other options in the trade market since the free agent market isn’t strong at the position. One player that could be available that makes a lot of sense is Orioles’ first baseman Ryan Mountcastle.
Mountcastle comes with two years remaining of control. He has the potential to almost seamlessly replace the void left by Walker and has enough remaining control to bridge the gap to prospects Gino Groover and Ryan Waldschmidt, although the latter projects for left field. It would also allow the team to give Smith the opportunity to grow into the DH role while backing up first base and an emergency option at both corner outfield spots.
While he hasn’t been great the past two seasons, sporting 4.6 bWAR/3.2 fWAR over that time, there is a case to be made there is more upside. Despite a lack of power, he has a .270/.317/.438 triple slash with only 31 home runs. However, his raw power suggests he’s capable of much more. He ranks in the 90th percentile in bat speed, 74th percentile in hard-hit rate (batted balls with an exit velocity of 95.0 MPH or more) and launch angle sweet spot, and 76th percentile in average exit velocity. Yet that has only translated to a barrel rate in the 58th percentile.
The lack of power doesn’t seem to come from his ability to hit the ball hard or hitting them at the right launch angles independent of each other, but rather his inability to do both with one swing. Two obvious issues come into play when looking at his batted ball data. Isolating just for hard-hit batted balls, the two biggest problems are too many of them have a launch angle less than 0° and he’s not getting enough of them into the ideal launch angle range of 20-32°. Mountcastle had a negative launch angle on 29.1% of his hard-hit batted balls and only 20.0% in the ideal launch angle range, significantly lagging behind the MLB averages of 23.4% and 22.7% in each category.
Those two particular launch angle ranges are very telling in terms of a hitter being able to get the most of their raw power. In 2024, MLB hitters batted .271 on hard-hit balls with a negative launch angle but only slugged .293, meaning most of those hits were singles. On the flip side, they hit .596 while slugging 1.954 on hard-hit contact in the 20-32° range, which is why so many of those particular batted balls get classified as a barrel.
Another area of concern, albeit a minor one if the D-backs can unlock more in-game power, is Mountcastle can be a free-swinger on offense. His chase rate consistently ranks in the bottom 10 percentiles and has always been below average in drawing walks. He drew them a career-low 5.3% in 2024. So naturally he best profiles as either the third or fourth hitter in the lineup, where his raw power has the best chance of making an impact on the scoreboard.
Over the years, Mountcastle has really made himself a solid defensive first baseman. Since taking over the position on a full-time basis in 2022, he has accumulated +4 fielding runs on Statcast and +9 fielding runs on Baseball Reference. Breaking down his outs above average profile, it’s clear that he is more comfortable ranging to his left rather than his right. His style is more suited towards taking away the first base line and playing from depth against left-handed hitters, ranking at +8 OAA vs. lefties and -3 vs. righties. If Shaun Larkin and the D-backs coaching staff can get him more comfortable taking away the 3.5-hole, he has the potential to earn some Gold Glove votes and perhaps take one home.
With a potential first base target that could be available in the trade market, the next natural step is asking what it would take to land him. The Orioles have a top prospect waiting for an opportunity in Coby Mayo, although he hit .098 in his first major league call-up. They could also consider moving Gold Glove third baseman Ramon Urias across the diamond and insert Jordan Westburg at third to fill the gap if they deal Mountcastle, so they can absorb such a loss without it affecting the team too much.
Calculating a potential trade surplus value is somewhat tricky. There’s still more upside to be unlocked with the bat, but he’s averaged less than 2.0 WAR between the two sites over the last two years. Steamer currently projects Mountcastle for 1.6 fWAR in 2025. Using that figure for both seasons, a dollar figure of $8 million per WAR, and salaries of $6.6 million and $10.0 million, his final surplus value adds up to $9.1 million. A good total, but nothing that the D-backs couldn’t afford to match.
One such option would be to trade staff ace Zac Gallen in his final year of control. Gallen is projected to be worth 2.9 WAR in his Age 29 season according to ZiPS while projected to make $14.6 million in his final year of arbitration. The spreadsheet value has Gallen at $9.0 million, although I think his trade value is significantly higher than that number. The Orioles of all teams would know the cost of a top-of-the-rotation pitcher with one year of control left, having traded Joey Ortiz and DL Hall to the Milwaukee Brewers for Corbin Burnes last winter. Given the likely prohibitive cost it would take to replace Gallen in the rotation, it simply isn’t worthwhile to deal him to another team and then try to stay competitive in 2025.
Other alternate options would be for the organization to deal from its outfield depth. Jake McCarthy is the D-backs’ best trade chip, and it could make sense to sell high on him, but it would take much more than Mountcastle to pry him away from Arizona. They could sell low on Alek Thomas, a career .226 hitter if they decide there is very little they can do to improve his batted ball metrics. Pitching prospects Cristian Mena and Yilber Díaz could also make sense although the dearth of major league ready starting pitching will make them cautious to include either of those two in a deal. However, I don’t necessarily think the D-backs will have too many issues meeting the necessary price to land Mountcastle from the Orioles if he’s their guy.
Michael McDermott has been writing about the Arizona Diamondbacks, and their minor league system, for 9 seasons for AZ Snake Pit, Diamondbacks on SI, and Burn City Sports. You can follow him on X at x.com/michaelmcdmlb or at Bluesky.