Mariners Sign Chris Flexen From KBO

Yesterday, the Seattle Mariners signed Chris Flexen to a two-year deal. The 26-year-old will earn $4.75 million in guaranteed money, with an option to make more if he hits certain innings thresholds. Per MLB Trade Rumors, the Mariners attached “a $4MM club option and, if Flexen throws 150 innings in 2022 or 300 frames from 2021-22, an $8MM vesting option.” The contract itself is a bit of a Dipoto special, as the Mariners used a similar structure when they extended Wade LeBlanc and amusingly tacked on three club options; none were picked up.

Getting back to Flexen, the right-hander spent 2020 in South Korea, but most fans will remember him from his time with the Mets. He last appeared on a prospect list back in 2017, when Eric Longenhagen hit the nail on the head with his scouting report:

“He sits 91-94, touching 96, with an average curveball and fringe change. He has a big, sturdy, inning-eating frame but has already had a surgery, and there are scouts who’d like to see if the fastball plays consistently at 96 out of the ‘pen. Others think he’s more of an up-and-down starter.”

While he debuted later that summer, the Mets ultimately rolled snake eyes on Flexen’s development. In 68 innings spread across three seasons, he posted ghastly numbers, running an ERA north of eight while walking more hitters than he struck out. It seems almost cruel to mention his home run problem at this point but, well, too late. Ineffective and out of options, Flexen faced a very uncertain future heading into 2020.

All of that made Doosan’s $1 million offer too good to refuse. Flexen didn’t fit the mold of a typical KBO pitcher, most of whom are 30-something journeymen looking for a steady paycheck. By big league standards, they usually come with underwhelming stuff (Jake Brigham), little prospect pedigree (Erik Jokisch), or both (William Cuevas). In Flexen, the Bears got an unusually promising arm, and gambled that his stuff was good enough to get KBO hitters out even if he was a little rough around the edges.

They bet wisely, as Flexen instantly became one of the best pitchers in the league. With an average big league fastball (about 92-93 out of the rotation) and three offspeed pitches that missed bats, Flexen bullied the competition, leading the league in K% while posting the circuit’s second-best FIP. A broken foot limited him to 116 regular season frames, but he was very good all year long, and deGromian after returning in September:

If anything, those numbers undersell how well he finished the campaign. In the regular season’s final month, he allowed three runs while striking out 42 in 31 innings. In the playoffs, he followed that up with a 1.91 ERA in 28 high-leverage frames. While teammate Raul Alcantara won the Choi Dong-won Award, it was Flexen who emerged as the ace of the staff down the stretch.

Still, most former big leaguers do well in Korea, and a good statistical season alone generally won’t attract MLB teams. Clubs become more interested when a pitcher’s success stems from some kind of adjustment, whether that be a new pitch, grip, arm slot or anything else that suggests things will go differently in a second spin through the majors.

Flexen didn’t change dramatically. He still works with four pitches out of an over-the-top arm slot, which he hasn’t tightened up. He throws about as hard as he did in the majors. We don’t have spin rate or spin efficiency numbers from the KBO, but to my eye the movement looked similar to his time with the Mets. The slider he used in his debut season has morphed into a cutter over time, but otherwise it’s the same repertoire.

As many have noted around the internet, the two things Flexen did tweak are how often he’s throwing his curve and where he’s locating it. The curve was a natural pitch to experiment with, as it has a very high spin rate (84th percentile in 2019, per Baseball Savant) and was underused in New York. In Doosan, he leaned on it as an out pitch, raising his usage from 3.6% with the Mets 13% last season.

Location wise, Flexen deployed his curve somewhat differently last season. In the majors, he’d sometimes use it to try to coax a batter down and out of the zone, but he would also try to steal a strike with it, and was prone to leaving it up when he didn’t finish the pitch.

Last year though, he used it almost exclusively as a two-strike chase pitch, and to very good effect: per Ben Howell’s indescribably good KBO statistical database, hitters whiffed against it 22% of the time he threw it and posted a .196 wOBA against it. The curve was far from his only weapon — all four of his pitches were effective — but hitters really struggled with it.

(That heat map also comes from Ben’s site which, again, is just an amazing resource for all things KBO.)

The tricky part to project is how well it will play against MLB bats the second time around. If the curve is the big differentiator between how he pitched two years ago and what he looks like now, it stands to reason that it will be a critical ingredient for him in Seattle. The discrepancy in how batters fared against the curve on each side of the Pacific is thus a matter of some concern, because while KBO bats couldn’t touch it, MLB hitters very much could:

Undoubtedly, some of the gap can be explained away by better location and Flexen’s increasing comfort with the pitch. Perhaps stemming from his low usage rate, the curve was an inconsistent pitch for him back in his Queens days. Occasionally he’d spin a nasty breaking ball, but he’d often miss badly or soften it up in an effort to find the strike zone, an approach hitters ruthlessly exploited.

The talent gap between leagues seems like a bigger factor, though. Intuitively, that makes sense: A mid-70s curve is a power pitch in the KBO but pedestrian velocity in the States. And even if Flexen has become more consistent with his curve and its location, we don’t know how often hitters will bite at a pitch that so consistently lands in the dirt.

Moreover, we also don’t know well the high-heat, low-curve tunneling approach Flexen used to great effect in Korea will translate either. It’s a good idea in theory, but low-spin 92 mph heaters up in the zone are a dangerous proposition at the highest level. At the very least, he won’t find himself in nearly as many pitcher’s counts even if he does have success with the curve.

It’s also worth noting that Flexen comes with a pretty lengthy injury history. The broken foot came from a well-struck line drive and was just a freak incident, but he hasn’t been durable. He’s already had Tommy John, has only topped 100 innings three times, and the 145 frames he chucked last year were a new career high. Mariners fans should not expect him to make 30 starts and fire 180 innings, as Merrill Kelly did when he moved from the KBO to the Diamondbacks.

Fortunately, the Mariners won’t be counting on him to do so. Beyond Marco Gonzales and Justus Sheffield, Seattle’s rotation is shaky but deep in arms you can dream on, with a couple of good prospects on the way to boot. In a year where the Mariners are not particularly well-positioned to make a run at the division, a volatile pitcher like Flexen makes a lot of sense: If his curve really is an out pitch now, and he works his way into the rotation, this will be a hell of a pickup for Seattle.

But even if he doesn’t, the downside is limited. The Mariners are committing less than $5 million here, chump change for any franchise. If he can’t crack it in the rotation, his fastball should play up into the mid-90s in short stints, which gives him a good shot to be an effective reliever, potentially in a multi-inning role. That would hardly represent a bad outcome, both for Seattle and Flexen. After all, scouts have been projecting something like that for years.