Seattle Mariners could go to a platoon in left field

The Mariners’ plans in left field have looked fairly straightforward since the team signed AJ Pollock to a one-year deal last month, but President of Baseball Operations Jerry Dipoto nonetheless confirmed to reporters last night that the expectation is for left field to a platoon between Pollock and one of Jarred Kelenic or Taylor Trammell (Twitter link via Ryan Divish of the Seattle Times).

Both Kelenic, 23, and Trammell, 25, are recent top-100 prospects who at one point were candidates to hold down long-term spots in the Seattle outfield. Kelenic, in particular, was touted as a potential star but has struggled in the big leagues to this point despite a .302/.372/.574 output in 537 plate appearances at the Triple-A level. His struggles against fellow lefties have been particularly pronounced, but Kelenic did turn in a .249/.330/.503 slash against right-handed pitching in 2022 (Triple-A and MLB combined). Trammell, meanwhile, hit .274/.365/.527 against righties between Triple-A and MLB. There’s some understandable hope, then, that a platoon arrangement with one of Kelenic/Trammell and Pollock (.286/.316/.619 against lefties in 2022) could form a productive tandem.

Trammell was heralded as the superior defender of the pair during his prospect days, though neither he nor Kelenic has posted standout defensive grades thus far in the big leagues. Kelenic has more experience in the corners and has drawn above-average marks for his work there. He’s also been more apt to barrel the ball and has been less strikeout-prone, though his 29.9% mark in the big leagues is obviously problematic.

Both Kelenic and Trammell were featured in a piece by Baseball America’s Kyle Glaser, wherein he polled scouts for opinions on some recent top prospects who’ve graduated to the Majors but struggled to establish themselves. Kelenic drew more praise between the two, particularly for substantial defensive improvements, but scouts who spoke to Glaser offered fairly bearish views of both players’ swings at this point. However, Mariners GM Justin Hollander said yesterday that hitting coach Jarret DeHart has been working with Kelenic and gone through a motion-capture breakdown of his swing this offseason, and the results have been “over-the-top awesome” (link via Corey Brock of The Athletic).

Both Kelenic and Trammell are still young, and it’s fairly common to see a swing change or mechanical adjustment bring about major turnarounds in a player’s outlook. The Mariners clearly aren’t giving up on either player yet, though with both entering their final minor league option year, this is a crucial season for Kelenic and Trammell. Should they falter, the M’s have another lefty-swinging outfield bat who’s nearly ready for a Major League look; 25-year-old Cade Marlowe is on the 40-man roster and turned in a combined .287/.377/.487 slash between 120 Double-A games and 13 Triple-A games in 2022.

Kelenic and Trammell aren’t the only once-vaunted Mariners prospects who’ve turned in shaky big league results to this point. Righty Matt Brash won the fifth starter’s job out of spring training in 2022 but was tagged for 17 runs while posting a 19-to-17 K/BB ratio through his first 20 innings (five starts). That prompted the team to option Brash back to Triple-A Tacoma, and when he returned in July, he was used exclusively as a reliever.

That’ll be Brash’s role in 2023 as well, Dipoto confirmed (Twitter link via Divish). It’s easy to see why the Mariners are intrigued by the switch. Brash has been a starter for most of his career, but he returned to the Majors and obliterated opposing lineups while working in short relief last summer; from July 9 through season’s end, the 24-year-old pitched to a 2.35 ERA with a huge 33.9% strikeout rate. His 12.6% walk rate still needs refinement, but Brash’s heater jumped from an average of 96.3 mph in the rotation to 97.8 mph out of the ’pen and his 14% swinging-strike rate was excellent.

It’s always possible that there will be rotation innings for Brash down the road, but the Mariners look to have several spots locked up long-term. Ace Luis Castillo signed a five-year, $108M extension after being acquired in a trade last summer, and left-hander Robbie Ray inked a five-year, $115M in free agency last offseason. Young arms Logan Gilbert and George Kirby, meanwhile, are controllable for another five and six seasons, respectively.

Both Gilbert and Kirby have made good on their status as former first-rounders and top prospects, quickly cementing themselves as high-quality big league hurlers. And, as Dipoto tells it, the duo won’t be facing any hard innings limitations in 2023 (via Brock). Gilbert threw 185 2/3 innings over the life of 32 regular-season starts in 2022, while Kirby notched a combined 156 2/3 innings between Double-A, Triple-A and the big leagues. Both pitchers turned in an ERA in the low-3.00s with sharp strikeout and walk rates (Kirby, in particular). The pair might be eased into spring work, but the goal seems to be for each to make a five-inning start in the late stages of camp, setting the stage for them to work without limits once the season begins.

The group of Castillo, Ray, Gilbert and Kirby is among the best rotation quartets in baseball, but the fifth spot in the rotation remains a source of at least some uncertainty. Seattle has a pair of candidates in Marco Gonzales, a mainstay over the past five years, and KBO returnee Chris Flexen, who’s posted a 3.66 ERA in two seasons since signing in Seattle. Both pitchers have been floated as possible trade candidates throughout the winter. Gonzales is owed a combined $18.5M from 2023-24, while Flexen will earn $8M in 2023 before becoming a free agent in the offseason.

There’s been little indication of serious trade talks involving either in recent weeks, but it’s certainly possible that another club will show increased interest once early-spring injuries inevitably begin to arise. Then again, having both on hand gives the Mariners themselves an important safety net in the event of an in-house injury, so there’s little pressure to force a deal if the return isn’t meaningful.