Is there any hope for Marlins' highest-paid reliever in 2025?

Just four months after inking South Korean right-hander Woo-Suk Go to a two-year, $4.5 million deal, the San Diego Padres were ready to cut their losses. Go was part of the package that the Miami Marlins received in exchange for Luis Arraez last May, but he wasn't an asset in the trade—the Marlins took on the remainder of his contract as a favor, enticing the Padres to part with better prospects than they would have otherwise (Dillon Head, Jakob Marsee and Nathan Martorella).

Following the trade, Go continued to underwhelm in the upper minors. After only seven relief appearances as a member of the Marlins organization, he was designated for assignment to create space on their 40-man roster. The Marlins would shatter their single-season franchise record by using 45 different pitchers in 2024, but he wasn't one of them.

Even so, the Marlins haven't entirely given up on Go yet. They owe him a $2.25 million salary in 2025 regardless, which is more than any reliever who's actually on Miami's roster. Before flushing that money down the drain, he's been given the opportunity to make another impression during spring training as a non-roster invitee to big league camp.

Go had seven seasons of professional experience in the Korea Baseball Organization before signing with the Padres, peaking as one of the league's best closers. And yet, he's still just 26 years old, younger than many of his fellow Marlins NRIs. Perhaps the team wouldn't be as patient with a comparable player who was already in his 30s. 

Coming over from the KBO, Go's fastball velocity was believed to be "sitting 93-95 mph, up to 98," according to a scouting report from Eric Longenhagen of FanGraphs. We didn't see that in stateside competition. His four-seam fastball only averaged 92.8 mph during Triple-A appearances, peaking at 95.7. It also had a relatively low spin rate of 2,120 rpm, which would have ranked around the 13th percentile of qualified MLB four-seamers last season, per Baseball Savant. With that pitch as his primary weapon, he struggled to induce swings-and-misses.

The table below is courtesy of Thomas Nestico's pitching summary app.

Go was victimized by ineffective defense in 2024. He posted a 6.54 ERA, but a substantially lower 4.87 FIP. It's reasonable to expect his .370 batting average on balls in play to improve even if he pitched in front of the same group of fielders moving forward.

That being said, a turnaround in luck would only take Go so far. The quality of the swings taken against him may also be an indication that he was too predictable.

Opponents loved ambushing Go on the first pitch of a plate appearance. When putting those pitches in play, they slashed .480/.500/1.040 with eight extra-base hits. Here's new teammate Eric Wagaman clobbering a belt-high fastball for a 422-foot home run.

Runners went 12-for-14 when attempting to steal bases against Go (an incredible throw by Will Banfield prevented them from going 13-for-14). It's not uncommon for relievers to be neglectful of men on base, but unless the quality of Go's stuff ticks up, he has little margin for error. He'll be allowing a lot of balls in play if ever summoned to the majors and those become more damaging when you're nonchalant about letting guys advance into scoring position.

Inviting Woo-Suk Go to big league camp is understandable when the Marlins truly have nothing to lose. However, after closely reviewing his previous campaign, I didn't come away with much reason to be optimistic. He doesn't have any sort of background as a starter and only topped out at two innings in his longest outings, making him an awkward fit even for mop-up duty.

The 2024 Marlins received solid bullpen production from some unexpected sources. Let's see if that trend continues into 2025 with Go.