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What’s Next for Zack Thompson?

I take a look at what Zack Thompson can do to improve after he established himself as the most reliable left-handed reliever in the bullpen last year.

Pittsburgh Pirates v St. Louis Cardinals Photo by Scott Kane/Getty Images

Zack Thompson’s first real exposure to professional hitters came in 2021 at the Triple-A level as he threw just over 15 innings after getting drafted in 2019 and didn’t pitch at all in 202 due to the cancelled minor league season. That’s an unusually tough assignment for a young pitcher and, perhaps predictably, it didn’t go well. But the lefty steadied himself in 2022, regained some velocity on his fastball, earned his major league debut, and then became the most reliable left-hander in the St. Louis Cardinals bullpen. (Something could probably be said for Packy Naughton, but a 4.78 ERA overshadowed his strong 3.14 FIP.) That’s one heck of a bounce-back season!

Zack Thompson is now 25 years old and heading into what should be his second major league season (unless the Cardinals want to send him down to Memphis to keep developing him as a starter). So, with that in mind, I want to take a look at what Zack Thompson can do to build on his solid debut season where he posted a 2.08 ERA and 3.89 FIP in 34 23 innings of work.

Better Fastball and Curveball Tunneling

The first thing that jumps out to me is Zack Thompson’s strikeout rate. His strikeout rate dipped from 29.4% in Triple-A to 19.9% in the majors and that, along with his arsenal, suggests that there are some more whiffs in the tank for the left-hander.

There’s a lot to like about Zack Thompson. He pairs above average velocity with borderline elite extension which really helps his fastball get on hitters in a hurry. He also has a go-to secondary offering as he can locate a big breaking curveball that averages 2800 rpms of spin. It’s really these two pitches that are the foundation of Thompson’s arsenal and, on paper, you’d think they would lead to more whiffs that he actually got last year.

So, even though Thompson was effective in 2022, that’s the real question for me. How does he get more whiffs? That’s really what will take him to the next level, so let’s see if we can provide an answer for this whiffs dilemma.

And really, I think the answer is two-fold. The first thing I want to see Thompson do is reign in his breaking ball. It averages 67.4 inches of drop (with gravity), which is a lot, but a lot of movement doesn’t always mean a lot of whiffs. In Thompson’s case, I think it actually hinders the amount of whiffs he gets.

Now, I’m not saying it’s a bad pitch. It fact, it’s the excessive amount of break that really causes hitters to beat it into the ground as it had a 58.6% groundball rate last year. But the problem is that it barely missed any bats. A 16.9% whiff rate is simply not good no matter how you slice it. If this is going to play like a plus pitch (which it certainly has the potential to do), then he needs to sharpen it.

I want to see the pitch move less, but it’s not just the movement I’m worried about; it’s the velocity too. This is a pitch that sits 75 mph with big break but I would rather it sit 78-79 with sharper break.

And I don’t think I’m alone in this. Thompson himself admitted it in an interview with Fangraphs when he said (about his curveball) “I try to tunnel it off my four-seam, but it’s still big enough that it’s not easy to tunnel.” And that right there is why Thompson doesn’t get whiffs. The curveball is so big that he has to start it too high for it to land at the bottom of the zone.

Here’s an example:

That’s a ton of movement and a pretty pitch but if he threw that harder and sharper, he wouldn’t have to throw the pitch so high for it to finish at the hitter’s knees. That would then make a fastball at the top of the zone more effective as it would make a cleaner tunnel with his fastball. Since he needs to start his curveball so high now, he also needs to throw his fastball up and out of the zone for it to be a perfect runnel and reach the maximum amount of deception. And that’s obviously not ideal.

A sharper curveball would help him tunnel both pitches better which should help him get more whiffs with both pitches. And that seems like an easier solution to me than trying to get him to add spin to his fastball and get a more dramatic rising effect.

But to begin with, Thompson could get more consistent with his pitch locations as his curveball can have a tendency to drift up in the zone while his fastball doesn’t live a the top of the zone like it should.

He would do better to really stretch the zone vertically and work his curveball at or below the knees and his fastball at or above the top of the zone.

Right now, I don’t think Thompson really has an “out” pitch. The curveball could turn into one and maybe even the high fastball too but, at the moment, his curveball is more of a solid early count/groundball kind of offering and his fastball is limited without good tunneling.

So, while, this is the biggest change I think Thompson needs to make to get more whiffs; I don’t think it’s the only one. The other problem with a fastball/curveball-only combo is that there’s a 20 mph velocity difference between the two pitches.

Changeup and Cutter Development

Thompson would benefit from establishing a reliable third pitch that can split the velocity difference and maybe even a fourth pitch to give him a pair of pitches to wrok in and out while his fastball and curveball work up and down. That would help him cover the whole zone effectively.

The good news is that he’s already shown some feel for a third and fourth pitch as he threw a changeup 8.3% of the time and a cutter 6.1% of the time last year. The changeup was primarily a weapon against opposite handed batters while he used his cutter almost exclusively against same handed batters.

Of the two my favorite is the cutter but both of them have potential and he should continue developing both of them to keep a starting job open in the future. And that development may continue more aggressively this year because he will have 22 games of MLB experience and a full offseason to make adjustments and because he will have a different catcher. Now, this is NOT a shot at the greatest defensive catcher of my lifetime but it is an observation that Yadier Molina has always seemed to call fastballs more aggressively with young pitchers.

I don’t know if that’s just a Yadi thing but I’ll be curious to see if that changes with Contreras. There a chance that a new catcher may be more aggressive with Thompson’s whole arsenal and give him the opportunity to throw a few more cutters and changeups.

For me, progress would be seeing Thompson throw a tertiary option at least 15% of the time in 2023. That would give him a solid foundation from which to keep building.

I am more inclined to believe that his changeup will be his go-to third pitch (even though I like his cutter better) simply because his cutter almost exclusively to same-sided hitters in 2022 and if he continues to pitch in multi-inning stints he will likely see more righties than lefties. I could be wrong because if the Cardinals and Thompson identify his cutter as his third best pitch then he should throw it more than his changeup. Regardless, let’s discuss the changeup first.

It’s a pitch that still needs some development as his feel for the pitch can be pretty good at times but his location was bit spotty. It doesn’t get a ton of movement in either direction but it’s not a pitch that relies on having a ton of movement. Rather, he does a good job of killing spin and he throws it hard which helps it gets some late fade and helps maximize it’s deception when it’s thrown well.

It has the potential to be a weapon against right-handers if he can get more consistent with it and not do this as often:

He doesn’t always miss this badly but he does miss somewhat often by a decent amount to his arm side. Getting the pitch more consistent is really the next step for him because it can be a nice little pitch when it’s thrown well.

The changeup has some potential but his cutter is really the pitch that I think can give him a third average or better offering (after his fastball and his curveball, of course). Now, Baseball Savant classifies the pitch as a cutter which is why I’m calling it a cutter but to my eye it looks more like a slider.

First off, that’s a lot of movement for a pitch that sits 88 mph and that’s why I like it more than his changeup. It’s not just about how much movement it has, either. Rather, it’s about the sharpness of the movement. I like that he throws it hard and gets sharp sweepy action.

(Also, it looks like it has more movement and a slightly lower velocity than I would expect of a traditional cutter thrown by someone with a 95 mph fastball which is why I think it’s a slider, but I digress.)

This is exactly the kind of pitch that Thompson needs to round out his arsenal. It splits the velocity difference between the fastball and the curveball and gives him a more horizontally-oriented pitch to give the hitter something extra to worry about.

He left that pitch over the plate a bit too much for my liking which gives it the opposite problem as his changeup. That’s something that can be overcome, though. Really, besides that I actually like the pitch and would love to see what it can do with more than 6% usage.

One of the things I really love about this pitch too is the tunneling possibilities with his changeup. His changeup doesn’t get a ton of run so he could keep it down and to his arm side while throwing his slider in the same spot and letting it run to the other side of the plate. The tunneling possibilities of those two pitches are limited if Thompson is going to keep them partitioned to righties or lefties exclusively, but it still works within his arsenal as whole.


Between the velocity and extension on Thompson’s fastball and his big breaking, high spin curveball, Thompson has two pitches that can really form the foundation of a solid arsenal. But he also throws a slider and a changeup that could both be decent options with more development.

He had a bit of a rocky minor league career but really steadied himself in 2022 and then became the ost reliable left-hander in the Cardinals bullpen down the stretch. I think he can build on that success and potentially even throw his hat in the ring for a starting job in 2024 in he can do a few things

  1. Sharpen his curveball
  2. Locate his fastball higher in the zone
  3. Improve his feel for a changeup
  4. Throw his cutter/slider and his changeup more

Doing these things would give Thompson a more diverse arsenal, better tunneling and the ability to effectively get to all regions of the strike zone.

Thanks for reading, VEB. I’ll be back on Sunday to take a look at another young player.