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Posted: Nos. 11-20
Nos. 21-30
Nos. 31-40

Wednesday: No. 5
Thursday: No. 4
Friday: No. 3
Saturday, Feb. 27: No. 2
Sunday, Feb. 28: No. 1
Monday, March 1: Best Tools
Tuesday, March 2: How many Mariners prospects would be No. 1 elsewhere?
Wednesday March 3: Projected 2024 Lineup, Rotation, Bullpen
Thursday, March 4: Projecting the Top 10 Prospects after the season

The Seattle Mariners farm system is as deep as it’s ever been. There’s big-league talent beyond the club’s Top 20. Below is prospects Nos. 11-20.

Important note: There’s a delicate balance between upside, risk, and ETA, but the difference between No. 10 and No. 5 or No. 6 isn’t as significant as it may seem in some cases.

6 George Kirby RHP 2023 COMMAND A+/AA
7 Taylor Trammell LF 2021 HIT AAA/MLB
8 Cal Raleigh C 2021 POWER AAA/MLB
9 Brandon Williamson LHP 2023 FASTBALL A+/AA
10 Isaiah Campbell RHP 2023 FASTBALL A/A+

10. Isaiah Campbell, RHP
Campbell has yet to throw a competitive pitch in pro ball but has size (6-4/230) and projectable command that should allow his four-pitch mix to work as a starter with a chance to move quickly.

It might make sense for the right-hander to focus on one of his breaking balls in 2021, and the slider is further along than his slow, somewhat loopy curveball which might be better used as an early-count eye-level changer than an out pitch.

He creates plane by staying on top of a high three-quarters slot and despite some barking about his long arm path throws strikes. There’s some tail to his fastball and he does a good job maintaining arm speed throughout his arsenal. Campbell is adept at attacking the entire zone.

The cub’s comp-round pick from two years back could start 2021 at either Class-A affiliate but has a chance to move up once or twice this season. As a starter he carries mid-rotation upside.


60+ (92-96) 50+ (80-83) 45 (71-75) 50+ (81-84) 50

9. Brandon Williamson, LHP
Williamson has been up to 97 mph with his fastball and carries a better set of secondary pitches than does Campbell. If he had more experience and was a step or two closer to the majors I likely would have him ranked 2-3 spots higher.

He’s athletic and uses his 6-foot-6 frame to pitch downhill with his fastball, curveball and slider, all of which project as big-league pitches.

The curveball is above-average and has a chance to be the best in the organization. His changeup needs a lot of work but has flashed near average and should at least be useful in time.

Williamson’s arm slot is around three-quarters, perhaps a bit lower, helping him create angles that prove difficult for both lefties and righties when he stays closed and explodes through release point. His fastball has life up in the zone and he uses it well on both edges to right-handed batters.

Williamson has a chance to be a very good No. 3, with good  fastball command and changeup quality his biggest hurdles. He should start 2021 in Class-A Everett with a shot to move up as the year progresses, and could easily speed up his ETA.


65 (93-97) 50 (84-87) 55+ (78-82) 55 (83-86) 45+

8. Cal Raleigh, C
Raleigh is never going to be mistaken for Yadier Molina or Pudge Rodriguez defensively, but he’s answered a lot of questions with playable answers, and offers the kinds of intangibles clubs want from catchers.

Raleigh is a tough leader, has improved his receiving and framing, and his above-average arm strength plays up with good accuracy and consistent mechanics. He’s worked hard to maintain his conditioning in order stay behind the dish.

His calling card, however, is power, showing legitimate 60-grade pop from the left side and fringe-average, doubles power from the right. He has average bat speed, but the swing is a bit long, so he’s likely to swing and miss quite a bit, with home runs as the payoff.

His left-handed swing is also his better side in terms of contact and hitting for average, though there hasn’t been any buzz about giving up switch-hitting, and it might be less than ideal to do it now when he’s so close to the majors.

Raleigh projects as an average catcher led by power hitting, but if the hit tool catches up a bit with experience he could see some DH time when he’s not catching, perhaps extending his career that otherwise could be shortened by a lack of athleticism.


40+ 60 45 55 30

7. Taylor Trammell, OF
His plus to plus-plus speed jumps out and he’s always shown an above-average ability to get the barrel to the ball. The bat speed suggests raw power into the mid-teens or better, but the attempts to unlock it appear to have hurt his ability to hit for average in 2019.

There’s still too much swing-and-miss in his game considering the more likely power production, which is the largest hurdle to his chances to hit big-league pitching. But he’s always drawn walks and provided value in the field and on the bases.

Trammell’s swing is still a work-in-progress and as a result I don’t have as much confidence as some regarding his ETA. I do, however, buy his defensive value more than most, even if his below-average arm keeps him in left field.

There’s some Starling Marte in Trammell’s upside, and some Jacque Jones in the median projection. It’s difficult to imagine he’s not a major-league player, considering the speed and defense. The exact role is yet to be determined.

He’ll start 2021 in Triple-A Tacoma, probably playing both center and left, and likely gets at least a cup of java with the big club later in the season.


55 50 50+ 40+ 60+

6. George Kirby, RHP
Kirby’s best attributes lend tons of confidence in his ETA and floor, led by plus-plus control, plus command and athleticism that helps him repeat his delivery very well.

The right-hander will cruise 91-94 mph but there’s more velocity to come based on the occasional 95 in college and his work at the alternate training site that produced a lot of 95-99 in the fall.

The four-seamer has life and run, and his slider, an above-average, 84-87 mph breaker, is his best chance to be a true swing-and-miss offering.

His changeup has flashed plus and I project it to land there in time, and he uses a 79-82 curveball effectively versus left-handed hitters, burying it below the zone or getting called strikes. It’s not as consistent or sharp as the slider, but should remain an early-count weapon.

Kirby projects as a No. 3 starter for me, and the floor isn’t much of a drop. I think there’s a decent chance he’s better than Logan Gilbert or Emerson Hancock, perhaps thrusting Kirby into No. 2 status, though I fall quite shy of seeing a No. 1 starter or true ace. I think he’s ultimately more than a command-and-feel right-hander who wins with efficiency.


60+ 60 50 60 65

11 Juan Then RHP 2022 FASTBALL A+/AA
12 Zach DeLoach CF 2023 HIT A+
13 Jonatan Clase CF 2025 RUN A/A+
14 Austin Shenton 3B 2022 HIT AA
15 Sam Carlson RHP 2024 FASTBALL R/A
16 Andres Munoz RHP 2021 FASTBALL AAA/MLB
17 Connor Phillips RHP 2023 FASTBALL R/A
18 Levi Stoudt RHP 2023 FASTBALL A/A+
19 Jake Fraley OF 2021 HIT AAA/MLB
20 Milkar Perez 3B 2024 HIT R/A
21 Ljay Newsome RHP 2021 COMMAND AAA/MLB
22 Anthony Misiewicz LHR 2021 CURVEBALL MLB
23 Will Vest RHR 2021 FASTBALL MLB
24 George Feliz CF 2025 HIT R
25 Braden Bishop CF 2021 FIELD AAA/MLB
26 Yohan Ramirez RHR 2021 SLIDER AAA/MLB
27 Joey Gerber RHR 2021 FASTBALL AAA/MLB
28 Adam Macko LHP 2024 CURVEBALL A/A+
29 Wyatt Mills RHR 2021 FASTBALL AAA/MLB
30 Sam Delaplane RHR 2021 CURVEBALL AAA/MLB
31 Carter Bins C 2023 FIELD A+/AA
32 Alberto Rodriguez OF 2024 HIT A
33 Aaron Fletcher LHR 2021 SLIDER AAA/MLB
34 Kaden Polcovich 2B 2023 HIT A/A+
35 Damon Casetta-Stubbs RHP 2024 FASTBALL A/A+
36 Michael Limoncelli RHP 2025 CURVEBALL R
37 Kristian Cardozo RHP 2026 CURVEBALL R
38 Starlin Aguilar OF 2026 POWER R
39 Tyler Keenan 1B 2023 POWER A/A+
40 Taylor Dollard RHP 2023 CHANGEUP A


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Jason A. Churchill

Churchill founded Prospect Insider in 2006 and spent several years covering prep, college and pro sports for various newspapers, including The News Tribune and Seattle PI. Jason spent 4 1/2 years at ESPN and two years at CBS Radio. Find Jason's baseball podcast, Baseball Things, right here.