The Mariners are filling out new manager Jason Kanzler’s coaching staff. The team on Monday announced the hiring of Tanner Swanson as its next bench coach and CJ Gillman as its next hitting coach.
Swanson, a Washington state native who graduated from Central Washington University, was on the Yankees’ Major League staff from 2020-26. He had served as New York’s director of catching since 2020 and was also its Major League field coordinator since 2024. Gillman was Seattle’s Minor League hitting coordinator from 2022-25.
Under Swanson, the Yankees have led MLB in catcher framing runs since 2020 (+86) and rank 11th in blocks above average (+5).
Swanson will replace Manny Acta as Seattle’s bench coach. The Mariners parted ways with Acta and three other coaches from former manager Dan Wilson’s staff at the end of the regular season. They also let go infield coach Perry Hill, hitting coach Kevin Seitzer and first-base coach Eric Young Jr.
Gillman, 37, left the Mariners in 2026 to become the director of hitting for the Nationals, who blossomed from one of the sport’s least effective offenses to one of its most productive. Washington was one of the sport’s surprise teams last season, in large part for how it swung the bat so well.
That, and more so, Gillman’s familiarity with so many of the Mariners’ young hitting core, were the likely driving factors to this hire.
Gillman was a guiding influence for many top prospects who’ve recently reached the Majors in Seattle, including infielder/outfielder Michael Arroyo, shortstop Colt Emerson, outfielder Lazaro Montes and second baseman Cole Young.
He also occasionally spent time in Seattle with the big league team during his previous tenure as a supplement to the coaching staff, most prominently after director of hitting strategy Jarret DeHart was fired in August 2024.
Moreover, Gillman could represent a philosophical shift in addition to being a familiar face.
“Multiple of our Major League players who came through our system have referenced what they learned in player development that got abandoned in the big leagues this year,” Mariners president of baseball operations Jerry Dipoto said in an end-of-season press conference.
“And not just the players who came up for the first time. We have a host of players who've come through our system, and they saw a difference. We need to get back to what we believe is a Mariners baseball process.”
Gillman, the Mariners’ new manager and the impending assistants to supplement the hitting side will be tasked with extracting more from an offense that saw a significant decline in just one season.
Mariners offense, 2026
BA: .233 (29th)
OBP: .314 (21st)
SLG: .379 (28th)
OPS: .693 (27th)
Runs/game: 4.10 (28th)
wRC+: 102 (10th)
K rate: 23.0% (24th)
The Nationals, meanwhile, ranked third in MLB in runs per game (5.07) and tied for third in OPS (.743).
Both hires come in the aftermath of the leadership shakeup that saw Wilson’s tenure as manager conclude along with four coaches from Wilson’s staff.
The departure of Seitzer, who was in his second season, followed that of assistant hitting coach Bobby Magallanes, who was let go on July 23. The Mariners retained all of their coaches on the pitching side.