The Mariners nab RHP Chris Flexen, one of the KBO’s best, on 2-year deal

With a rotation that currently features three pitchers that I don’t particularly trust, I have been patiently waiting to see how the Mariners address the rotation this offseason. It’s far from their greatest weakness — in fact, it’s currently their greatest strength. Nevertheless, I’ve holding out hope that the Mariners would acquire something resembling a frontend pitcher. Sonny Gray would be cool. Zack Wheeler, too. Joe Musgrove is probably the most ideal to me. Try again! The Mariners have reportedly signed Chris Flexen to a two-year deal for $4.75 million.

You may remember Flexen best as the swingman who was really, really bad for the New York Mets. Over 68 innings, he posted a 8.07 ERA with a -1.5 K-BB% — you read that right, -1.5 K-BB%! — and 6.92 FIP. That’s very bad! As you can imagine, Flexen took 2020 as an opportunity to recoup some value and sign with the KBO’s Doosan Bears, where he posted a 28.0 K% and 2.74 FIP over 166.2 innings. In the context of MLB, that’s great, but here’s a tweet via KBO enthusiast Ben Howell showcasing just how dominant Flexen was:

This is awfully impressive, given that Hyun-jin Ryu is perhaps the greatest starting pitcher in KBO history — and if he’s not, he’s certainly one of the best since 2002. The interesting (and perhaps troubling) thing is that Flexen didn’t make very many significant changes during his time with the KBO. Perhaps most notably, he went from MLB (where his velocity is mediocre as a starter) to the KBO’s second-hardest throwing starter.

He continued to throw his fastball around 60% over the time as he did with the Mets in 2019. His fastball’s swinging-strike percentage increased from his MLB career 6.3% to 12.2% in 2020. He doubled it! His fastball velocity matched his average from 2018 (92.6 mph), but was down from his 94.3 mph average in 2019 out of the bullpen, so we can chalk some of his increases in whiffs to pitching against lesser competition.

But most notably, he started throwing his curveball about 13% of the time, a large increase from his 4% in 2019. Metrically, his fastball and curveball are both solid pitches on their own. From a pitch tunneling perspective, they form the strongest pairing of any of his pitches.

Here’s a fastball-curveball overlay, courtesy of Ben Howell (once again!):

We know that you don’t have to have a Gerrit Cole fastball for it to work above the zone. Despite middling velocity and even worse spin, Flexen’s fastball features strong ride due to its spin axis and spin efficiency. This is why he’s able to lean on a fastball-heavy approach.

There are a few issues present, though. The first is that he doesn’t throw his curveball very much. He should do that more! While I’m generally not a fan of slower curveballs — those are generally used as get-me-over pitches to steal strikes — Flexen has one that has a monster amount of drop. It’s suited perfectly for the above approach: fastballs up, curveballs down.

As mentioned above, he leans on a fastball-heavy approach, using it to pitch away from batters of both handedness. This is why his repertoire centers around it. As is, there are three starting pitchers who threw their fastball 60% of the time or more: Austin Voth, Daniel Ponce De Leon, and Tyler Glasnow. Obviously, he’s going to need to throw more secondaries as he transitions back into MLB. This is something that I’m sure he’s aware of and will address upon returning to MLB. Regardless, it’s always a plus to have a solid fastball to build around, and he’s got a solid one.

Here’s one of his dominant outings in a short clip:

He tops out around 93 mph here, but Flexen showcases his whole package here. He uses his fastball upstairs, which allows him to drop his curveball underneath the zone, and throw his slider off the plate to his glove-side. What he doesn’t flex here is his changeup that produced an 18.5% swinging-strike percentage and 33.8% CSW in 2020.

Now, all four of Flexen’s pitches sat around 30% CSW this past year. That’s really good! The thing is, as a starter, I think we’d see those numbers take a healthy tumble. The fastball and curveball can probably maintain their respective 29.8% and 31.0% CSWs, but his slider and changeups have garnered too many called strikes for me to believe that they’d translate to MLB. As a reliever, I think he can maintain many of these numbers. He wouldn’t have to worry about seeing hitters a second or third time as much, and he’d be able to hold velocity over the duration of his outings.

And so, overall, by pitch characteristics, there are a few pitchers that I think Flexen could strive to be. As a starter, I don’t think Flexen is dissimilar from Zac Gallen, albeit in a lesser form and drastically different arm slot. Their repertoires are similar enough. Gallen’s are simply much more refined, and his changeup is plus to plus-plus. In almost all certainty, Flexen is lesser across the board and as a whole. What remains to be soon is how much lesser.

The other pitcher is Seth Lugo. Again, his repertoire is vaguely similar, but he throws out of a similar slot too. Lugo fits the profile of someone who is extremely valuable as a multi-inning guy in the bullpen and somewhere around league average as an occasional starter. It’s unclear whether Flexen is destined for the rotation — I imagine he gets a look at the very least — but he seems like a strong fit in the bullpen.

And so, it remains to be seen how the Mariners plan to deploy Flexen. Out of the rotation, he’s plenty interesting. Out of the bullpen, Flexen could be quite good. It would be disingenuous to suggest that he can be Gallen or Lugo, so I don’t want anyone to come away thinking that. And it’s pretty likely that he’ll be far from the pitcher he was in 2020. At the very least, however, he’s more interesting than whoever his replacement would be in the rotation or bullpen. And that’s enough for me.