MLB’s September roster expansions are almost here, and the Seattle Mariners will surely be using their additional two roster spots to try and bolster their push for the playoffs.
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Teams must call up two additional players Sept. 1 when rosters across the league grow to 28 players. They can not carry more than 14 pitchers, but they can carry over 14 position players.
With some concerns at the back end of the bullpen, the M’s appear primed to add one pitcher and one position player Monday. Here’s a look at who Seattle could call up during September.
Position players
• Could we finally see the MLB debut of top catching prospect Harry Ford? Ford has raked in Triple-A all season long, batting .289 with a .411 on-base percentage, .880 OPS and 34 extra-base hits (including 16 home runs).
The M’s have faced a bit of a conundrum when it comes to promoting Ford, as there just isn’t any playing time to spare at catcher with Cal Raleigh and Mitch Garver in the fold. That’s still the case now, but perhaps the Mariners could find some playing time for Ford in September when carrying three catchers would be easier. That could allow Raleigh a few more DH days before a potential playoff run without having to start Garver more against right-handed pitching, which Ford has excelled against (.913 OPS) in Triple-A.
• Ford would be the exciting promotion, but utilityman Samad Taylor and infielder Leo Rivas make more sense for this roster. Both would be solid options off the bench as pinch-runners, and both could give rookie second baseman Cole Young a day off against left-handers in lieu of Jorge Polanco, who has fared much better against right-handers this season and grades out as a below-average defender.
Taylor, at least initially, is probably the favorite here since he also plays the outfield. Right fielder Victor Robles still has a 10-game suspension looming, which he will begin serving once his appeal has been ruled on. If Robles is forced to miss time in September, Taylor gives the Mariners a right-handed bat who can play the outfield. He is hitting .308 with an .871 OPS and 16 home runs with Tacoma, which includes a .341 average, .955 OPS and seven homers against southpaws.
Rivas has already made an impact at the big league level this season, posting a .411 on-base percentage in 30 games with the Mariners. He’s continued his strong year in Tacoma, batting .307 with a .460 on-base percentage, .955 OPS and 10 home runs for the Rainiers. The switch-hitter also excels most against lefties, posting an .829 OPS versus southpaws in the majors and 1.084 OPS in Triple-A. Additionally, Rivas provides some shortstop depth behind J.P. Crawford.
A situation where Taylor comes up while Robles serves his suspension and Rivas replaces Taylor when Robles returns seems plausible.
• Third baseman Ben Williamson has a strong case of his own to rejoin the big league club. He played 85 games while serving as the starting third baseman in the majors for over three months this season, regularly flashing exceptional defensive skills while doing so. He’s also shown a little more pop since being sent down to Triple-A (four home runs in 16 games).
Those are all good reasons to believe Williamson could get the call in September (and he very well could), but the fact he has continued to stick at third in the minors suggests he’ll stay in Tacoma until this season is over, barring an injury in the majors. If we were seeing Williamson deployed around the field in the minors to prep for a utility role in September, he’d be the heavy favorite on this list.
BEN WITH HIS FOURTH BLAST!! pic.twitter.com/d25zpSLoGL
— Tacoma Rainiers (@RainiersLand) August 24, 2025
• It seems unlikely, but second baseman Ryan Bliss could factor in here, too. The 25 year old was Seattle’s starter at the keystone on opening day before suffering a torn left biceps that has kept him out since April.
Bliss began a rehab assignment with Tacoma on Thursday night. General manager Justin Hollander last week said the plan was for Bliss to get 40 to 50 plate appearance once he started a rehab stint. The timeline will be tight, as Bliss will surely get some days off during rehab, but his speed could be an asset to the big league club.
• Utilityman Miles Mastrobuoni is also worth mentioning here due to the speed, defense and positional versatility he provides, although Taylor and Rivas seem to be more likely candidates since they excel against left-handed pitching – an area the Mariners have had troubles lately.
Pitchers
• The Mariners called up Emerson Hancock on Wednesday. He would have been the clear favorite to be the September pitching add otherwise. But there is a good chance multiple arms will cycle through the Mariners’ bullpen in the final month, which would likely mean at least the temporary returns of right-handers Jackson Kowar, Casey Legumina and Sauryn Lao.
Both Kowar and Legumina struggled before recently being sent back down to Tacoma. Lao, who was optioned when Hancock was recalled, has pitched in just two games in the majors this year. Each are capable of covering multiple innings.
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• Right-hander Gregory Santos will be a player to monitor over the next few weeks, as he could potentially return in mid-September. The flamethrowing Santos, who has pitched just 16 games in two seasons with the Mariners due to multiple injuries, has been out since April while recovering from knee surgery. Hollander said last week Santos was expected to start a rehab assignment soon, but that hasn’t happened yet.
If Santos can provide the Mariners with something close to what they expected when acquiring him in a trade before last season, he’s very likely the most impactful pitcher they could add from within the organization.
• Another name to keep an eye out for is veteran right-hander Michael Fulmer. The M’s signed the 2016 AL Rookie of the Year and former All-Star to a minor league deal last week. He’s allowed one run and struck out five over four innings in four appearances with the Rainiers.
After missing all of 2024 following UCL revision surgery, Fulmer appeared in a combined three major league games for the Red Sox and Cubs this year. The 32 year old posted back-to-back sub-3.50 ERA campaigns out of the bullpen in 2021 and 2022.
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