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Seattle Mariners Sleepers: Eye For The Future With Justus Sheffield, Logan Gilbert, Evan White & More

The Seattle Mariners are brimming with up-and-coming prospects and that's on full display within SI Fantasy expert Shawn Childs's list of five sleepers from the Emerald City.

Sleeper: SP Justus Sheffield

After looking close to the majors after pitching well at AA and AAA in 2018 (2.48 ERA and 123 Ks over 116 innings), Sheffield ended being a bust for any fantasy owner thinking he would help in 2019.

His season began with four reasonable starts at AAA (3.93), but he walked 14 batters over 18.1 innings. The Seattle Mariners gave him one start in late April (two runs, seven baserunners, and four walks over three innings), before shipping him back to AAA.

He pitched so poorly in nine starts (8.35 ERA and 1.991 WHIP), the Mariners had to drop him in class to AA. Sheffield regained his form over ten starts (1.49 ERA, 0.9949 WHIP, and .218 BAA over 66.1 innings with 71 Ks).

He struggled over his next four games between AA and the majors (7.20 ERA and six HRs over 20 innings). Still, Sheffield did get a taste of success in two games with Seattle (one run over 11 innings with 11 Ks) before running off the tracks again over his final three starts with the Mariners (11 runs and 23 baserunners over 13.2 innings with 15 Ks).

His AFB (93.1) was league average while working off three pitches (four-seam – .284 BAA, slider – .302 BAA, and changeup (.320 BAA).

Over six seasons in the minors, he went 43-33 with a 3.31 ERA and 640 strikeouts over 620.2 innings.

This year I’d like to see more life on his fastball, and growth in his command (3.5 walks per nine in his minor league career). Worth a flier and follow based on his ADP (416). Possible help in strikeouts with plenty of WHIP risk earlier in his career.

READ MORE: Mariners Will Not Play First Two Series at Home

Deep Sleeper: 1B Evan White

Despite having 18 career at-bats at AAA, the Mariners signed White to a $24 million contract in November for six seasons.

Last year he hit .293 over 365 at-bats at AA with 18 home runs and 55 RBI while missing some development time due to a hip injury in April. His bat did shine in June (.371 with eight HRs and 19 RBI over 97 at-bats).

Seattle drafted him with the 17th pick in the 2017 MLB June Amateur Draft after played well over three seasons in college (.356 with 17 HRs, 109 RBI, and 18 SBs over 655 at-bats).

Over two-plus seasons in the minors, White hit .296 with 32 home runs, 133 RBI, and seven stolen bases over 906 at-bats. His strikeout rate (20.4) and walk rate (8.6) should be favorable in the majors.

While his contact batting average (.392) grades well, but his swing path may produce a high number of ground balls earlier in his career. White did have a high HR/FB rate (19.4) at AA.

I’m getting a John Olerud feel here. White has a plus glove with more underlying power. Based on his new contract and no one blocking him at first base, he should be in the major early in 2020 if he doesn’t make the team out of spring training.

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A reasonable chance at a .280/20/80 player out of the gate while his power may be better than expected in year one of his pro career.

His ADP (402) puts him in the free-agent pool in most 12-team leagues.

Deep Sleeper: OF Jake Fraley

Over the past two seasons, Fraley proved he could handle AA pitching (.313 with 11 HRs, 47 RBI, and 16 SBs over 230 at-bats) while receiving 152 at-bats at AAA in 2019 (.276 with eight HRs, 33 RBI, and six SBs over 152 at-bats).

His walk rate (7.9) and strikeout rate (20.8) came in about the league average in 2018 and 2019. Seattle gave him 40 at-bats late in the year, but Fraley looked overmatched (.150 with 14 strikeouts).

His season ended in September with a right thumb injury. This season he’ll battle Kyle Lewis for the playing time in right field. Fraley offers a competitive, balanced skillset once he proves he can handle major league pitching. Player to follow this spring while having an ADP of 540.

Deep Sleeper: SP Justin Dunn

Over the past two seasons, Dunn spent most of his time at AA (15-10 with 3.82 ERA and 263 Ks over 221.1 innings). In 2019, he showed growth in both his walk rate (2.7) and strikeout rate (10.8), helping him to four appearances in the majors.

With Seattle, Dunn walked nine batters over 6.2 innings, but he only gave up two hits and two runs with five strikeouts.

His AFB (92.6) wasn’t an edge in velocity. Batters did have a tough time hitting his four-seamer (.125 BAA) and slider (.100 BAA) while throwing minimal changeups.

A developing arm that will need some time at AAA. Dunn will get plenty of strikeouts with more upside when he throws more strikes. Possible fast mover in 2020 and a must follow through spring.

Deep Sleeper: Logan Gilbert

Seattle drafted Gilbert with the 14th overall pick in the 2018 MLB June Amateur Draft. He is on the fast track to Seattle after pushing his way from single-A to AA in his first year in the minors.

Over his last two seasons in college, he 21-2 with a 2.41 ERA and 270 strikeouts over 201.1 innings.

After five great starts at A-Ball (1.59 ERA and 36 Ks over 22.2 innings), Gilbert held form at High A (1.73 ERA and 73 Ks over 62.1 innings). His arm did perform well at AA (2.88 ERA and 56 Ks over 50 innings).

In the end, Gilbert tossed 135 innings with a 2.13 ERA and 165 strikeouts. His walk rate (2.2) was elite, along with his strikeout rate (11.0).

I expected him the majors by June with a chance to offer playable innings for fantasy teams. Keep a close eye on him as the Mariners may push him quickly with only a half-season of action in 2020. 

READ MORE: 2020 Seattle Mariners Fantasy Team Preview

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