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Breaking Down Offseason Targets - Relievers Part 1

I’ve seen a few names connected to the Cardinals recently so I wanted to take a deeper look at them.

MLB: ALCS-Texas Rangers at Houston Astros Erik Williams-USA TODAY Sports

Recently I’ve seen a few relievers being connected to the St. Louis Cardinals, which makes sense. The team has already added 3 starters to their rotation and they still need to address the bullpen so I would be shocked if the Cardinals tried to secure a reliever or two soon while also big game hunting in the trade market (or the Yamamoto market) at the same time.

The biggest potential target I haven’t covered in my breakdown series is probably Dylan Cease, and even though I‘m not writing about him today, I will write about him soon. It’s the reliever market that has me interested. It started moving recently as the Reds have already double dipped with both Emilio Pagan and Nick Martinez while the Dodgers are working to secure terms with Joe Kelly.

For a Cardinals team that has struck quickly this offseason, I wouldn’t be shocked in the slightest if the Cardinals tried to fortify their bullpen quickly. The good news is that I’m not shooting blind in this piece. The Cardinals have been linked with at least 3 names so far so those are the ones I want to cover today.

Those names are Phil Maton, Woo-Suk Go, and Yuki Matsui.

The report on the Cardinals’ varying levels of interest comes from Derrick Goold of the Post Dispatch, who is one of the few sources of information that I trust completely at this time of year.

Here’s what he had to said about the trio in his latest piece:

On Phil Maton:

The Cardinals have expressed some interest in right-hander Phil Maton, who spent recent seasons as a steady presence in Houston’s playoff-bound bullpen. Maton, 30, grew up in Chatham, Illinois. In his past 200 games he’s pitched 198 1/3 innings with 232 strikeouts and a 3.86 ERA.

On Yuki Matsui:

The Cardinals also have scouted Yuki Matsui, a lefty reliever with more than 200 saves for Rakuten in Japan’s highest league. The standout 28-year-old reliever does not require a posting fee after a season with a 1.57 ERA and 72 strikeouts in 57 1/3 innings.

On Woo-Suk Go:

KBO closer Woo-suk Go, a right-hander, is also exploring a jump to the majors and reports in Korea have linked him to the Cardinals.

To be fair on that last bit on Woo-Wuk Go, the reporting is coming from Korea and not Goold directly so I have no idea how accurate that reporting is. Regardless, he’s still worth breaking down.

Let’s get started with Phil Maton before moving to the duo of Asian relievers.

Phil Maton

Phil Maton is really weird and I love him for it and, selfishly, I hope the Cardinals sign him because he’s just so interesting. I mean, the guy can really spin a breaking ball. And a fastball for that matter.

In fact, of all pitchers who threw at least 100 curveballs last year, Maton’s spin rate ranks 4th at 3156 rpms. He also finished top 15 in fastball spin (2565 rpms) and also throws a sweeper that averages 2685 rpms of spin. So, yeah, Maton is a real spin-machine.

The best part is that he uses that spin to get a lot more whiffs that you would expect from someone of his velocity profile.

For example, Maton’s four-seamer averages 89 mph. yet it registered a whiff rate of 32.3 mph in 2023. I’ll get more into how that happened later. For now, what I want to talk about is Maton’s breaking balls because not only are they impressive, but they’re also his primary pitches.

The curveball is his most heavily used pitch overall at 40.4% and he uses the pitch a ton against left-handed hitters. In fact, that usage rate rises 52.1% when the batter has the platoon advantage. Against righties, Maton turns to all 3 of his top pitches at a pretty equal rate but his sweeper usage edges out the usage of the other two offerings.

So he’s a primary breaking ball pitcher and that works in his favor. That also means that he’s not a power pitcher. Instead he harnesses his ability to generate spin in order to create movement and stay off the barrel while also missing a good amount of bats.

Maton’s 27% strikeout rate is a solid figure but it’s not a sign that he completely overpowers hitters. That’s why it helps for him to a 99th percentile average exit velocity allowed. So, not only does he miss bats (90th percentile whiff rate) but when he can’t miss the bat, he generally creates weak contact. That’s a great pairing of skills.

It’s his combination of movement and command that makes Maton so effective. The most obvious example of this is with his curveball, which he can throw to both his arm side and his glove side. He like to focus the pitch on his glove side most of the time but against lefties, Maton will show off his command of the pitch and move it to both sides of the plate which makes the pitch especially effective (.236 wOBA, 36.4% whiff rate)

This is what his heat map looks like :

Here’s an example of the curveball at work:

It’s a sweepy affair with the pitch getting as much sweep as Maton’s sweeper but also much more depth. Despite the lack of velocity (73.8 mph on average), the pitch is incredibly effective and grades out really well according to stuff+ (131). He throws it a ton and he should.

The sweeper wasn’t as effective but still generated whiffs at a nearly 30% rate and likely profiles better than its .340 wOBA as the pitch’s .275 xwOBA tells a different story about its effectiveness.

The realsy interesting pitch is the four-seamer as it doesn’t profile as a bat missing offering and yet it is. The pitch gets very little ride and has a cut/sink shape at a low velocity and yet Maton throws it up in the zone. That’s not typically a profile that you would expect to play well at the top of the zone but I suspect that it’s mostly due to how he tunnels the pitch with his breaking offerings and uses the pitch as his secondary offering.

To give the specs on Maton’s fastball, he averages 24.3 inches of sink (10.2 inches of IVB) and 4.2 inches of run. That comes with a 50% spin efficiency which means that Maton creates a lot of gyro spin on his fastball which gives hitters a different look from the average major league fastball.

Stuff+ doesn’t think highly of the pitch (51 stuff+) but that doesn’t matter in the slightest. The pitch has proven to be able to miss bats and get good results and that matters way more than a stuff+ grade that doesn’t rely on a hitter’s input. And what I mean is that a hitter will tell you if a pitch is good and Maton’s fastball is good.

As a whole, I really like the arsenal and the combination of skills that Maton provides. He will also be 31 years old next year so I don’t imagine he will get more than a 2 or 3 year contact at most. That’s a signing I hope the Cardinals make.

The good news is that I think the Cardinals are pretty likely to sign him. They’ve been open about signing players who want to play in St. Louis and signing players who are from the area. Maton at least fits the criteria of being from the area and there’s already been reporting of the Cardinals interest.

So, of the 3 relievers I’m covering today, this is the one I’m giving the highest chance of signing with the Cardinals and I like that because I think Maton is not just good but also fascinating.

Yuki Matsui

Now we’re getting into some pitchers who don’t have as much publicly available information. What I can offer is some information on Matsui’s arsenal and his some information about his NPB stats.

I’ll start with the stats to help give a picture of how successful he has been.

At 28 years old, Matusi is coming off a season in which he posted a 1.57 ERA and struck out 32.4% of the batters he faced. That came with a walk rate of just 5.9% and a home run rate of 0.5 home runs per nine innings. Those last two figures aren’t as impressive in the contact-oriented NPB but they are still significant.

Add on the fact that Matusi has been dominant in each of his last 3 seasons and it appears that the lefty is ready for the jump to the major leagues.

That means that we should examine his arsenal.

I don’t have any pitch specs but I do have the eye test and I can say that Matsui’s fastball plays well up in the zone and that’s due to two factors, namely his good riding life but also do to the fact that he has a flat vertical approach angle due to his his height, or lack thereof (5’8”). The pitch sits mostly in the low 90s but can reach the mid-90s and should continue to play well at the top of the zone in the majors due to it’s characteristics.

The real story with Matusi is with the splitter, though. The pitch is his go-to secondary offering and generates a ton of whiffs. It’s an easy plus pitch and gives him a platoon-neutral pitch to boot. The problem is that it may not translate well.

Here’s what a recent MLB Trade Rumors article had to say about Matusi and his splitter:

Matsui’s small role in the WBC could have been due to reported difficulty he had throwing the WBC ball, which was larger than the standard ball used in NPB play and closer to the type of baseball used in the majors.

The ball used in the major leagues is, in fact, bigger than the ball used in the NPB so if Matsui is going to struggle to grip his splitter, which requires great finger separation, then the pitch may not translate well, which would obviously be a problem for Matusi and whichever team signs him.

Here’s my take on that. If the Cardinals are going to sign him then they are going to know how well he can grip a splitter with a major league ball. That’s called doing your homework. They can literally just give him an MLB ball and watch him try to grip it.

So, if the Cardinals feel comfortable about his ability to throw the pitch then so do I. They have more information than I do so I’ll follow them on this one. There’s really not another way for me to figure out Matsui’s splitter.

Here’s the pitch in action:

The final pitch in the arsenal is a sweepy slider which is a clear third pitch for Matsui in terms of usage but it looks like it profiles well with a good amount of sweep and depth. I wouldn’t be shocked if he used the pitch more in the majors and especially against righties.

Taken as a whole, I like Matsui, A lot depends on his ability to throw the splitter but if he can then the lefty has an effective platoon-neutral pitch to get righties out. That’s huge. The other issue is the size of the contact. Matsui is still just 28 years old so I wouldn’t be shocked if he received a 3-year contract worth around 7 million on average.

That’s not a huge contract but I’m generally not a fan of spending a ton of money on relievers due to the volatile nature of the position. So a contract like this would probably carry a little extra risk considering he’s never pitched in the majors before and may or may not be able to grip his splitter on a major league ball.

If Matsui’s splitter doesn’t translate then he proabably shouldn’t be given that 3-year deal. So, I’m fascinated to see how this turns out. If the splitter does translate then I like Matusi a lot and I think he could be a good #1 lefty bullpen option with a good fastball, a good secondary pitch against lefties (the slider) and a good secondary pitch against righties (the splitter).

I’m interested in Matsui but I also want to know more. The kind of contract he gets in free agency should give us the information that we need to know how teams feel about his ability to throw a splitter in the major leagues,

Woo-Suk Go

Woo-Suk Go is the biggest enigma on this list. Matsui may have a big question mark with his splitter but he at least dominated NLB competition. The same can’t be said for Go.

The right-hander posted a 3.68 ERA in the KBO in 2023, a league which is generally considered to be worse than the NPB and probably compares to about a Double-A level of talent.

That’s a bit concerning. So is that fact that he walked 11.6% of the batters that he faced. So, those are the reasons to be wary. He has good stuff that profiles well but he hasn’t been all that consistent of a KBO reliever and can struggle with control so he’s a tier below Maton and Matsui in my mind.

I do want to mention that Go apparently struggled with injuries in 2023 and that likely affected his performance so his 1.48 ERA in 2022 may be a better representation of his talent. I simply haven’t watched him enough to have a feel for that.

Go’s control was also better in 2022 as well as he “only” walked 8.8% of the hitters he faced that year while fanning 33.3% of them.

Let move into the profile now. The righty likes to throw his fastball, which can reach 98 mph but generally sits 93-95 mph according to Fangraphs and it too plays best at the top of the zone with it’s riding action and its low vertical approach angle.

The pitch may not have overwhelming velocity but I would expect it to miss bats at the major league level.

The other two pitches in Go’s arsenal are a cutter and a curveball.

Here’s an example of the curveball:

And here’s some video from Go closing out a game this year:

That’s some good looking pure stuff. The fastball has some riding and running action to it and the curveball has sharp 12-6 movement. I would expect Go to continue missing bats in the major leagues.

What is also interesting is that Go has generated a ton of groundballs in Korea, working his way to a 65.8% ground ball rate in 2023 so if he can miss bats and keep balls on the ground, he could have a lot of success,

My concerns with Go are with the slight hump in his curveball that makes the pitch more obvious out of the hand and with his lack of consistency and occasional control issues in the KBO. I don’t doubt that his stuff is good. Rather, I do question if he’ll be able to consistently throw strikes at the major league level when he is facing more advanced hitters and I do question if his curveball will be as dominant in the major leagues.

With that said, it’s pretty easy to envision a version of Go that is missing bats and keeping the ball on the ground and that would make him an effective reliever. I’m not out on signing him at all, rather I just think he has more risk of not panning out. That means he shouldn’t get a contract like Matusi.


I wish I had more information to offer on the two Asian pitchers but it’s hard to get pitch data from the NPB or KBO. That makes these two pitchers a little more mysterious than Maton but that’s okay.

Maton is my preferred option of the 3 with Matsui probably ahead of Go. The issue with this kind of assessment is that I don’t know what any of the 3 pitchers will cost. I would assume that Maton will require less of a commitment which suits my preferences when chasing relief pitching and I won’t pretend that that influences my opinion of the 3 pitchers.

With that said, if the Cardinals feel good about Matsui’s ability to throw a splitter with a major league ball the I can get behind his signing. He’s been a consistently excellent bullpen arm in Japan for a few season now and misses a lot of bats while limiting his walks.

If the Cardinals feel good about the scouting work they have done on Matusi then they could give him 3 years and really get some value out of his contract. I would be fine with a singing like that.

It’s Go that is the true wild card. I simply don’t have enough information on him but I can say fairly confidently that I would prefer Maton and/or Matusi.

That all depends on price of course, but, the report about Go claims that he isn’t necessarily guaranteed to play in the majors this year and that might mean that a team needs to bid a little higher than the market value on Go to convince his KBO team to allow him to leave.

Because of this and the fact that Go is still just 25 years old I would expect a multi-year deal for the relievers perhaps worth a little bit more than I would be comfortable paying considering the other options on the market. If the Cardinals want to shy away from that level of commitment, I don’t blame them.

The Cardinals have singed plenty of pitchers from Asia in recent years though so I wouldn’t be shocked if one or both of Matsui or Go ended up in St. Louis next year. The good news is that the trio of pitchers is exciting, has bat missing stuff, and should offer plenty of upside to the bullpen at a reasonable cost.

Thanks for reading, VEB. Hit the comments to let me know your favorite bullpen targets and have a great Sunday!