Seattle Mariners Breakout MLB Prospects For 2025

Breakout Prospects

Tai Peete, OF

Preseason Rank: 14
BA Grade/Risk: 50/Extreme

Track Record: Peete was a prominent two-way player coming out of the Georgia high school ranks in 2023. The Mariners took him with their competitive-balance pick after the first round and decided that his future was in the field, where his athleticism was too valuable to waste. Peete was initially drafted as a shortstop, but the Mariners have already started experimenting with him at third base, left field and center field. He put together a solid .269/.343/.408 batting line for Low-A Modesto in his first full season.

Scouting Report: Peete is still very raw, but he will at times show flashes of all five tools. His hit tool is the one most in question. He struck out over 30% of the time in 2024. Peete has a tendency to drift and lose his front side at the plate, and the lefthanded hitter will also bail with his front side versus southpaws. That also bleeds into his power output as well. Despite requisite size and natural strength to hit for power, he has yet to show much in-game power, often being too out-front and off-balance when he contacts the baseball. Still, evaluators are optimistic that Peete will eventually hit for average or better power. In addition, he sees a lot of pitches and walked over 10% of the time in 2024. He is a fluid mover on the bases who shows easy plus run and the baserunning instincts to go with it. He stole 45 bases in 50 attempts in 2024, and that should translate to some degree at higher levels. Defensively, it’s looking more likely that his future home is in center field. His jumps still need work, but his routes and closing speed are both excellent. As a former pitcher, his arm plays well in the outfield. He has the tools to stick at shortstop, but he boots too many plays, and arm accuracy has been a major issue for him thus far.

The Future: Peete is a longer-term project, but his ceiling is very high. He has the athleticism to develop into a do-it-all center fielder. He will likely head to High-A, where he could spend the majority of 2025.

Scouting Grades: HIT: 40. POW: 50. RUN: 60. FLD: 50. ARM: 60.

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Jeter Martinez, RHP

Preseason Rank: 15
BA Grade/Risk: 50/Extreme

Track Record: The Mariners signed Martinez for $600,000 in 2023, giving him the largest bonus for any prospect from Mexico in that signing class. He dominated the Dominican Summer League in his pro debut and followed that up with a decent 2024 season in the Arizona Complex League, albeit one littered with control issues.

Scouting Report: The appeal for Martinez begins with projectability. He’s 6-foot-4, athletic and has the room to add muscle, and his fastball already sits in the mid 90s and has touched as high as 99 mph. Martinez also shows the ability to manipulate the baseball, mixing in a two-seamer when he needs a ground ball. His slider shows good shape, but he struggles to locate it. His changeup will also flash solid armside run but lacks consistency and command. The bugaboo for Martinez remains his inability to pitch backwards or stay in the zone often enough. His control was fine for the DSL, and there are other scouting indicators that his control should improve in the future, but it remains the main roadblock to a future as a long-term starter. He walked nearly 17% of ACL batters in 2024.

The Future: Martinez has all of the ingredients to be at least a mid-rotation starter if he can rein in the walks. He is still incredibly young, ultra projectable and has the makings of three average or better offerings. There is a chance that he remains in extended spring training to spend extra time with player development, but he will likely be looking to make his full-season debut at some point in 2025.

Scouting Grades: FB: 60. SL: 55. CH: 50. CTL: 45.

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Teddy McGraw, RHP

Preseason Rank: 20
BA Grade/Risk: 50/Extreme

Track Record: McGraw has had two Tommy John surgeries, one in high school and one at Wake Forest. Despite going under the knife in his draft season, the Mariners were enamored enough with his arm talent to take him in the third round in 2023. McGraw came back from his surgery in 2024 to appear for 8.2 innings and showcase his electric stuff before being shut down for an elbow flexor injury.

Scouting Report: The main concern with McGraw is health, because he looks like a top-of-the-rotation starter when he’s healthy. His fastball is 94-98 mph with sharp, late armside run. Both of his secondaries are plus pitches as well. His slider is a sharp lateral breaker that destroys righthanded hitters, while his changeup shows late dive and fade away from lefties. He showed scattered control at Wake Forest, but he doesn’t need to be pinpoint with the quality of stuff that he possesses.

The Future: McGraw’s start to 2025 is uncertain because of his flexor injury. He has thrown just 8.2 innings in two years. He has an ace ceiling, and he’d be much higher on this list if health were not a concern. Still, he is a long ways away from the bigs and needs as many innings under his belt as possible.

Scouting Grades: FB: 60. SL: 60. CH: 60. CTL: 45.