Precocious outfielders Jarred Kelenic and Julio Rodriguez soak up most of the attention accorded to Mariners prospects, and rightfully so. They rival White Sox sluggers Luis Robert and Andrew Vaughn as the best position prospect duo in the game and should provide a needed boost to Seattle's offense when they arrive at T-Mobile Park in the next couple of years.
• Mariners Top 30 Prospects list
But Kelenic and Rodriguez also overshadow a burgeoning group of mound prospects in the Mariners system. Seattle has a pair of Top 100 Prospect arms in right-handers Logan Gilbert and George Kirby, their first-round picks in the last two Drafts, and several intriguing pitchers behind them.
"This is pretty exciting with our pitching depth," said Mariners vice president of scouting Tom Allison, who joined the organization in September 2012. "When I first rolled in here, we had a healthy Danny Hultzen, Taijuan Walker and James Paxton. The industry would say those three were highly touted.
"But our overall pure depth and the pure depth of near big leaguers and the next waves, it's the best since I've been here. We saw a lot of interesting performances this spring, not just stuff but also location and development."
Gilbert was the 14th overall pick in 2018 and he probably wouldn't have lasted that long if his velocity hadn't dropped while he dealt with mononucleosis during his junior season at Stetson. Seattle delayed his pro debut until 2019, when he excelled with a 2.13 ERA, .198 opponent average and 165 strikeouts in 135 innings while advancing from Class A to Double-A at age 22.
• Q&A with Logan Gilbert
Gilbert's best pitch is a 92-97 mph fastball that plays up thanks to the extension he creates with his 6-foot-6 frame. His curveball, slider and changeup all show flashes of becoming solid offerings.
"Logan was probably one of our top three players in the Draft coming out of the summer after what he did in the Cape Cod League," Allison said. "The mono really made it much easier for us to get him. You look at his extension, and his 92 plays like 97 and beats every barrel."
The 20th overall choice last June, Kirby led all NCAA Division I pitchers in strikeout/walk ratio (17.8) and walk rate (0.6 per nine innings) last spring for Elon. He continued to fill the zone in his pro debut, fanning 25 without issuing a walk in 23 innings at Class A Short-Season Everett. His precision control gets the most notice, but he also has a legitimate four-pitch repertoire highlighted by a fastball that reaches 98 mph.
"He just doesn't throw balls and pounds the strike zone," Allison said. "He's up to 98 and he's got a really good breaking ball. He just went out and did his thing during the summer, and that only punctuated what we saw in the spring."
Behind Gilbert and Kirby, there are 16 more pitchers on the Mariners Top 30 Prospects list. Of the 18 total arms, all but two have joined the organization in the last three years.
Allison said the Mariners decided if they were going to take on risk in the 2019 Draft, they were going to go with pitchers, and they spent their first five choices in the top four rounds on college right-handers Gilbert, Brandon Williamson, Isaiah Campbell, Levi Stoudt and Tim Elliott. They also gambled their sixth-round pick on prep righty in Michael Limoncelli, a top-three-rounds talent who slid after having Tommy John surgery.
Jerry Dipoto has also acquired several pitching prospects in trades. Former Top 100 Prospects Justus Sheffield and Justin Dunn arrived in deals following the 2018 season that sent Paxton to the Yankees and Robinson Canó and Edwin Díaz to the Mets (who also surrendered Kelenic in that transaction). After shipping strike-throwing righty Juan Then to the Yankees in November 2017 as part of a deal for Nick Rumbelow, Dipoto got him back last June in exchange for Edwin Encarnación.
Three of the better sleepers among Mariners pitching prospects signed in 2017. Right-hander Sam Carlson received an above-slot $2 million bonus as a second-rounder only to miss the next two years following Tommy John surgery, but he looked good this spring. Venezuelan left-hander Brayan Perez is unusually polished for a 19-year-old, while 23rd-round steal Sam Delaplane was one of the best relievers in the Arizona Fall League last offseason.
The Mariners currently have the longest playoff drought in baseball at 18 seasons. If all goes according to plan, Kelenic, Rodriguez and their pitching depth will lead Seattle back to the postseason in the near future.
Gilbert made his pro debut in big league camp a year ago and got pasted for five runs while recording just two outs. He looked much more in control this time around, allowing just one hit in four scoreless innings while striking out four. Manager Scott Servais noted the exceptional extension in his delivery.
After getting tagged for a 5.50 ERA in eight late-season appearances with the Mariners, Sheffield looked more confident this spring. He struck out 12 and walked just one while allowing two runs in eight innings.
Prospect we'll be talking about in 2021
The prize of Seattle's 2018 international class, shortstop Noelvi Marte signed for $1.55 million out of the Dominican Republic. He dominated the Dominican Summer League in his 2019 pro debut, batting .309/.371/.511 and leading the Rookie-level circuit with 54 RBIs and 134 total bases at age 17. He's on the same path as Rodriguez and should raise his profile once he plays in the United States this season.
Allison said one club official compared Marte's offensive upside and defensive profile to that of a young Hanley Ramirez.
"His bat and power will carry him," Allison said. "When we first signed him, I didn't think he could stay in the infield, but I watched what player development did with him and how he committed to a throwing program, and he's much more in sync and throwing better now. It's plus run and plus arm and he has actions, so I'm now convinced he could stay in the infield, possibly at third base if he continues to grow."
Something to prove
The Mariners hoped Sheffield would replace Paxton in their rotation early in 2019, but his control disintegrated and he got rocked for a 6.87 ERA in Triple-A during the first half. That necessitated a demotion to Double-A, where he relocated the strike zone, but he battled the location of his pitches in seven late-season starts with Seattle.
Sheffield's stuff also regressed last year, with his fastball residing in the low 90s and his slider showing fewer flashes of becoming a wipeout offering. He often looked more like a long reliever rather than the No. 2 or 3 starter he once projected as.
While Sheffield is still just 23, he faces an uncertain future as he enters his seventh pro season. The Mariners are encouraged that he arrived in Arizona this spring with a much more mature approach, which translated into positive results on the mound.
"When he walked into camp, there was a difference in everything he did," Allison said. "There was an intent in the way he went about his bullpen, the way he went about his high-performance and weight-room work, the way he prepared and scheduled his day. It was more like a big leaguer than a prospect.
"We saw some development with his changeup last year, and now his velocity is better and his command is better because of his confidence. We saw more conviction and location with his stuff this spring."
Jim Callis is a reporter for MLB.com. Follow @jimcallisMLB on Twitter. Listen to him on the weekly Pipeline Podcast.