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Takeaways from Matthew Liberatore’s and Zack Thompson’s first MLB stints.

I dive into what we have learned from the rookie southpaws in their first MLB stints and where they can improve.

MLB: St. Louis Cardinals at Philadelphia Phillies John Geliebter-USA TODAY Sports

The St. Louis Cardinals have had so many young players have success in St. Louis this season it’s kind of absurd. Donovan, Yepez. Gorman. Fernandez. Oviedo. These guys all either established themselves this year after early big league struggles (Oviedo, Fernandez), or hit the ground running in their debuts (everyone else).

Two former first round lefty arms have also made their debuts this season - Matthew Liberatore and Zack Thompson. Both have been returned to Triple-A, but one of them perhaps unjustly. (Note: Thompson has since returned to St. Louis. He was in Triple-A at the time of writing.)

That provides the occasion for my examination of the two pitchers. What have we learned? How can they improve? Have their results been surprising? Let’s find out!

Matthew Liberatore

We’ll start with Liberatore since he debuted first. Here are his stats after 27 innings pitched.

So, that’s not great, but let’s not overreact to a 27 inning sample. Liberatore is still a good pitcher and there are some clear (and achievable) ways for him to improve.

The most obvious is for Liberatore to find the strike zone. This happens often with young pitchers. They come up and nibble around the edges of the zone or too often throw out of the zone to try and get the hitter to chase instead of simply attacking the plate.

It’s tough to blame them for that. I mean, Major League hitters are better than Triple-A hitters and hittable pitches tend to get punished more at the highest level. Still, MLB hitters don’t just hit balls better, but they also tend to see the ball better. It’s usually harder to get an MLB hitter to chase. Thus, chasing chases only leads to walks for a young pitcher.

This describes Liberatore perfectly. The lefty has only thrown 44.5% of his pitches in the strike zone, which is 4% below average, and he’s thrown 45.6% of his pitches on the edge of the plate, which is 3% above average.

(In case you’re wondering how Liberatore’s edge rate can be higher than his zone percentage, it’s because, according to Statcast, pitches are considered on the edge if they are within one ball length of the edge of the zone. Thus, not every pitch included in Liberatore’s edge rate is a strike.)

This isn’t the whole story because some of Liberatore’s pitches simply weren’t competitive, but it does seem that he was really trying to keep the ball away from the heart of the plate at the expense of throwing strikes in his first stint with the Cardinals.

Living on the edges is never a bad idea, but Liberatore needs to trust his stuff more. He has pretty much always been a pitchability prospect, so walking 11% of the batters he faces isn’t going to be easy for him to overcome, especially since he’s not a groundball extraordinaire (35.6 GB%).

Simply telling a pitcher to throw strikes isn’t the most helpful thing in the world. It’s much easier said than done, but Liberatore has a long history of strike throwing. I’m not worried about it.

I think his walk issues are less because of a lack of ability and probably more because of a cautious approach. Attacking the zone should help him a lot and let him strut his stuff a little bit more.

Speaking of his stuff, let’s examine some of the Statcast data for his offerings.

Liberatore’s curveball looks like his best pitch. It has above average movement in both directions, a 79th percentile curveball spin rate (2713 rpms), and the highest whiff rate of any of his offerings. It has allowed an unimpressive .327 wOBA, but the pitch’s .246 expected wOBA is more promising.

This curveball looks like it will be Liberatore’s bread and butter pitch throughout his career.

Determining a pitcher’s best pitch isn’t exactly straightforward, or even helpful very often, but I think it’s pretty clear when it comes to the Cardinals’ top pitching prospect. That doesn’t mean his other pitches aren’t good too. In fact, one of the reasons I like Liberatore’s curveball is because of how well it plays off his fastballs.

I guess it’s cheating to call his curveball his best pitch if one of the reasons it’s so strong is because of his other offerings, but I’m going to do it anyways because I can. You’re welcome.

Just realize that when I say it’s his best pitch, it’s heavily dependent on his other pitches. I’ve said it before, but really, when it comes to a pitcher’s arsenal, nothing can be considered in isolation.

Besides the great movement on Libby’s breaker, the curveball tunnels beautifully with his sinker and four-seamer, and I especially love when Libby uses his four-seamer and curveball in tandem. It’s such a good one-two punch.

HIs sinker and four-seamer have the exact same spin (11:00) and his curveball is 6:00 away, meaning that it looks the exact same. That’s deception. But it gets even better. Look at where Liberatore throws his pitches, specifically his four-seamer and his big curveball.

That’s called tunneling. The high four-seamer sets up the curveball brilliantly because the two pitches have the same spin and start in the same spot before the curveball dives and the four-seamer stays up.

It’s clear that Liberatore really knows how to pitch.

Liberatore’s curveball isn’t his only quality breaking pitch. He also has good results on his slider (granted, in a small sample size). It doesn’t have crazy movement, but again, he knows how to use it.

I already showed Liberatore’s four-seam location above, so here’s his sinker location (which is a bit unusual) and his slider location.

Again, that’s brilliant. His slider doesn’t move much horizontally, it just drops almost 35 inches, which means that it pairs well with inside fastballs.

Don’t let Liberatore’s subpar results make you think he isn’t a good pitcher. He was the top ranked pitcher in the system and a top 100 prospect for a reason. He’s a really smart pitcher and he knows how to use his whole arsenal in tandem. That’s really impressive for a young arm and it means that he’s not far from being a productive arm.

The negative in Liberatore’s arsenal is that his fastballs aren’t overly impressive by themselves. Both his sinker and his four-seamer have below average velocity, movement, and spin. Neither pitch has had great results either.

I think he would be better off throwing fewer fastballs and letting his more impressive breaking pitches work. The fastballs should be used to set up his breaking balls. They shouldn’t be treated as weapons on their own.

55.2% of Liberatore’s pitches at the Major League level have been fastballs, with 30% being four-seamers and 25.2% being sinkers. That needs to change because Liberatore’s curveball is a thing of beauty and his fastballs are nothing speical. Not only is his breaker beautiful to watch, but also all the underlying metrics support it’s effectiveness. His slider seems like a solid pitch too considering its 2500 rpms and tunneling possibilities.

Quite honestly. I would like to see him throw his secondaries more than his fastballs. That’s atypical for a young pitcher, but it would allow Liberatore to be more effective. That’s how his arsenal is built.

The southpaw has given up a lot of hard contact, to the point where his Statcast page is filled with dark blue, and it’s the fastballs that have allowed the most damage. Simply throwing fewer could help him immensely.

Before I move on to Thompson, I also want to note that I’m generally not a huge fan of high sinkers. I’m not ready to apply that thought to Liberatore, though. I think his sinker could actually work best up in the zone where it could tunnel with his other offerings, so I’m willing to wait and see.

Zack Thompson

Zack Thompson is a bit different from Liberatore because he’s actually been productive this season.

Despite that, he pitches in a similar way to Liberatore with his high fastball and curveball combo.

Those two pitches have almost exactly the same amount of horizontal movement. The difference is that Thompson’s curveball drops a lot more (it also drops a half inch more than Liberatore’s).

This location combination is as good as Liberatore’s and Thompson also adds a perfectly located changeup to top things off.

This is great. Thompson can start each pitch in the same spot and they will each move to different locations. It’s a great way to pitch, and again, it’s really smart. And, also like Liberatore, his arsenal is focused on the top of the zone. His fastball stays up there, and then for deception, he starts most of his secondary pitches high and lets them drop into the bottom of the zone.

Liberatore and Thompson pitch similarly in that regard but a difference is that Thompson works the outer half of the zone much more often.

Liberatore likes to stay inside to right-handers, but Thompson’s heat maps are more focused on the outer half. That has worked well for him and he’s limited the damage that has come from pitches in those areas. It also makes me wonder if Liberatore would be better suited keeping his fringe-average fastballs away from hitters. I think he might be.

Where Thompson isn’t quite as good as Liberatore is in matching spin. Both his changeup and his curveball are close to being perfect mirrors with his four-seamer, but they aren’t quite there.

That’s something that Thompson could refine to give himself better deception. He’s really close, so its not like he would completely need to reshape the pitch, but changing the spin of a pitch is something easier said than done. He can’t just flip a switch, but it’s something that would be beneficial for him to work on.

Also like Liberatore, Thompson’s slow curve, which is thrown around 74 mph, has above average drop. Thompson pairs that with a fastball with a decent amount of zip, averaging 94.3 mph (61st percentile), and it looks like his four-seamer/curveball combination will be his bread-and-butter. That’s a good base to work from. The pitches compliment each other well.

One of the biggest surprises for me has been seeing Thompson pound the strike zone. That’s a big reason why he’s been better than Liberatore as 55.2% of his pitches have been in the zone with 48.2% being on the edge. Both of those rates are well above the league average.

Thompson has some control issues in 2021 but even after he rebounded in Memphis this year, I wasn’t expecting him to throw this many strikes. I don’t know if he’ll continue at this rate, but it’s an impressive start, and I’m encouraged enough to think that he can consistently run a league average walk rate, if not slightly better.

Thompson has also surprised me with his inability to generate whiffs thus far. He had a 31.3% strikeout rate in Memphis and that really has not carried over to St. Louis. He has a good curveball and a fastball with above average velocity that he throws up in the zone (which is usually where pitchers get whiffs), so it’s interesting to see that he’s not getting whiffs or strikeouts.

Perhaps his slow curve is a bit too slow, making it more geared for weak contact than whiffs (similar to Adam Wainwright’s), but I still think it should have better than a 12.5% whiff rate.

I also know that Thompson also throws a slider/cutter that Baseball Savant classifies as a cutter, but he’s only thrown five this year in the majors. Maybe adding a harder breaking pitch could play off his slower breaking pitch and lead to more whiffs.

I really don’t think Thompson should be a fastball pitcher. Quite honestly, it’s an average pitch that ticks higher when the velocity ramps up a bit but there’s nothing super intimidating about an average moving, low spin, 94 mph fastball. It’s a little bit of a different story when he touches 96 or 97 mph but that doesn’t happen all that often.

Like Liberatore, he’s going to be at his best when he’s really working his secondaries. He can probably get away with more fastballs than Libby can, but I would really love to see him work his curveball, changeup, and cutter/slider thing more.

Better mirroring could also help him improve and I think the biggest thing for him is going to be finding more strikeouts, but I’m not too worried about that yet since he got a ton in Triple-A.


Liberatore and Thompson share a lot of traits. Both are former first round picks, both are lefties, and both have debuted this year. Where they differ is in fastball quality and early results.

Even though Thompson has been much better than Liberatore, he’s come up in the ‘pen and Libby has fought things out in the rotation. Don’t let Liberatore’s struggles concern you too much. He’s a good pitcher and still has a bright future ahead of him.

Rather, let his struggles serve as a reminder that prospects don’t always come up and kill it. Even highly touted ones. Too often, prospects are expected to be the next big thing as sonn as they debut. Sometimes they need time to get broken into the big leauges and oftentimes too much is expected of a prospect.

Take Liberatore, for instance. He’s probably going to a be a 3 or 4 starter in a good rotation depending on how he develops. He’s not an ace (however you want to define what an ‘ace is). His fastball simply isn’t good enough for him to be an ace.

Despite that, he can still be a productive pitcher who carves out a solid role in the rotation. Him becoming a 3 or 4 starter shouldn’t be seen as a disappointment. Rather, it should be seen as a success because he would be filling a valuable role.

An ace is really hard to find. Expecting top pitching prospects to be aces is doing them a disservice. It sets the bar too high and makes a 4th starter look like a disappointment, when in reality, it’s a win for everyone involved, from the scouting department, to the player development staff, to the player himself.

Also, it’s really hard to find a true ace, or even a true top-of the-rotation guy, if he doesn’t have a plus fastball. Pitchability guys, or even guys with average fastballs aren’t typically top of the rotation arms. Sure, there’s some exceptions, but those are exceptions that buck the general trend; they are not the trend themselves.

So, in short, don’t be expecting Libby or Thompson to be top-of-the-rotation arms. That doesn’t mean they aren’t good. In fact, even though Liberatore hasn’t been good this year with St. Louis, there are still a lot of things to be encouraged by. His numbers have been ugly but I don’t think he’s super far from being a contributor. A few tweaks and I think he’s there.

Thompson, on the other hand, has already been good in a bullpen role and he belongs on the major league roster, not in Memphis.

Thanks for reading and enjoy your Sunday! It’s a busy week with the draft and the All Star break, so we have plenty of content on deck. Have fun watching the All Star festiviteis and may Monday end with an Albert Pujols home run crown!