by Micah Greenhill

The CastiWoes: What’s Wrong with Luis Castillo?

*sad sigh* Castillo, don’t go breaking my heart. One of the first posts I wrote this season was a piece oohing and awing over the pitching excellence of Luis Castillo. So far, the 28-year-old right-hander has not made me look smart. In spite of his ace-level pitching the last couple years and being pegged as a sleeper 2021 Cy Young candidate, Luis Castillo has had a horrible start. His troubles continued last night against the Rockies. Castillo pitched only 3.2 innings and gave up 8 earned runs.

Reds fans are asking: What’s wrong with Luis Castillo?

Past Performance vs. 2021 YTD

Let’s start unraveling this mystery by looking at Castillo’s past statistics and comparing them to what he’s put up so far this season.

Alright, let’s break this down. Some things jump off the table immediately. First is Castillo’s ERA. ERA is not a good stat for measuring starters, but it does provide a grounding to discussion and shows why Cincinnati is so disappointed in his performance this year. His FIP paints a slightly more optimistic tale. FIP is a helpful stat that operates on the same scale as ERA. It measures a pitcher’s ability to limit runs by looking at the three true outcomes (strikeouts, walks and home runs) and assumes an average defense behind the pitcher. With a FIP almost two points lower than his ERA, we can conclude that Castillo has had a bit of bad luck, which should normalize over the course of the whole season. Even with this bit of good news, Castillo’s FIP is still much higher than what is typical for him.

The difference between Luis Castillo’s 2021 and past seasons shows up in more than just in ERA and FIP. His walks and strikeouts per nine innings also tell story. Over recent seasons, Castillo has had a walk rate that is average or slightly worse. During a small sample size of 2021, he’s actually reduced walks. This coincides with a dramatic decrease in strikeouts and provides a theory as to why Castillo is struggling. He’s simply throwing the ball in the zone too much, and hitters are taking advantage of it.

Going Deeper

To figure out why Castillo has been struggling, let’s move past more traditional stats and start looking at advanced metrics.

So there’s good news and bad news here. The good news is that Castillo has been underperforming his peripherals. The bad news is that his peripheral metrics are still bad. Weighted on the same scale as ERA, his xERA, xFIP and SIERA are dramatically worse than previous seasons. This has directly impacted his xwOBA. In short, he’s not missing bats and hitters are achieving excellent quality of contact against him.

Batted Ball Data

So far, we have learned that Castillo is walking fewer hitters, but he’s also allowing more balls to be put in play. This isn’t always a bad thing, provided the pitcher is inducing weak contact and is supported by a strong defense. Neither of these have been the case for Castillo this year. Let’s take a look at his batted ball profile.

This data shows a logical explanation for Castillo’s struggles. Essentially, hitters are barreling more pitches than in previous years. This is resulting in harder contact, as indicated by an uptick in average exit velocity. When hitters are not striking out and they’re hitting the ball hard, we expect to see an increase in expected batting average and slugging, which is the case here.

Let’s review what we’ve learned so far. He’s not striking people out, and hitters are getting better quality of contact than in his previous seasons. All of this data is fairly self-explanatory and what one might assume given Castillo’s performance this season, but we still do not understand why Cincinnati’s ace is struggling so much.

Pitch Tracking

I’m going to warn you in advance. There are a lot of numbers about to come at you.

Okie dokie, what are we looking at here? For starters, we can see which pitches have been working for Castillo and which have not. His changeup, for example, is still getting good results. With an xBA and xSLG of .229 and .266 respectively, Castillo is still inducing a lot of weak contact from this pitch. The biggest difference is the whiff percentage. What was once among the most dominant strikeout pitches in the league simply isn’t getting as many swinging strikes. A likely explanation is that Castillo is just throwing this pitch much more because it’s the only pitch still getting results. During the 2020 season, Castillo turned to his changeup 30% of the time, but so far, 38% of his pitches have been changeups. His changeup relies heavily on deception, so the more he throws it, the more hitters know how to adjust. The success of the changeup is also determined by how it is set up by the fastball.

When looking at Castillo’s pitch mix, it’s clear the culprit for his struggles is not necessarily his changeup. It’s everything else, with the worst results coming from his sinker, which is getting hit hard and often. When not throwing a changeup, Castillo is averaging an expected slugging percentage of .601 on his pitches. That’s awful. When he’s throwing one of his three alternate pitches, the batter suddenly turns into Mike Trout. Obviously, these results are concerning, but we still don’t know why one of baseball’s more unhittable pitchers all of a sudden can’t miss bats. We have to dig deeper.

Location, Location, Location

We’ve discussed in depth already how Castillo is struggling to strike hitters out, but let’s revisit Castillo’s walk rate. From 2020 to 2021, Castillo has improved his walk rate from the 55th percentile to the 70th percentile. While this is a great improvement, it also may be an indicator that Castillo is throwing to many pitches in the strike zone.

Castillo’s pitching repertoire revolves around setting up deceptive pitches with a blazing fastball, so let’s start here in our study of why he is struggling so much.

The 4-seam fastball tends to have the most success when it is thrown at the top of the strike zone with a high spin rate. Essentially, the ball is too fast for a batter’s eye to track, so their brain creates a mental “forecast” of where the ball will end up. When thrown high in the zone and paired with a strong spin rate, the pitcher creates the optical illusion of a rising fastball, which induces many swinging strikes.

Unfortunately for Cincinnati, when Castillo throws a 4-seam fastball, it is missing both of these critical ingredients. While he does throw at an elite velocity (88th percentile), he has a below average spin rate (44th percentile). We can also look at the heat map and see that he’s throwing his fastball in the middle of the strike zone.

Essentially, what we have here is a non-deceptive fastball thrown down the middle of the strike zone at an elite velocity. Is it any wonder that batters are squaring up the ball and hitting it hard?

Let’s take a look at how his fastball has been moving lately.

Like his changeup, his 4-seam fastball is moving very similarly as it was last year. It’s falling slightly lower into the strike zone and has less horizontal movement on it. It makes sense that this has become a more hittable pitch. It’s moving in a straighter line and is going straight down the middle of the strike zone. The spin rate on this pitch is improved slightly, up to 2,275 RPM from 2,188 RPM. It’s still not an elite spin rate. In the past, Castillo has compensated for this by throwing the ball harder. This year, the average MPH is down from 97.4 to 96.4. In the past, Castillo’s velocity kept him alive with this pitch. Now, with a slower velocity, less movement and being thrown right down the middle of the strike zone, this pitch is getting hammered.

Let’s take a look, starting with his signature pitch, the changeup.

During the 2020 season, Castillo’s changeup tended to hit the bottom left hand side of the strike zone, but also had range to drop out of it. The largest difference this year is that Castillo is throwing the changeup lower, and a little bit more in the middle of the plate. It makes sense that throwing a deceptive pitch more often and putting it in the middle of the plate would lead to more contact.

Let’s take a look at how his changeup is moving compared to last year.

Overall, not much has changed in terms of movement. It’s dropping slightly more and breaking slightly less, but overall, this is the same changeup as last year. Even the spin rate is very similar (2010 RPM vs. 1949 RPM last year). However, because this pitch relies so heavily on deceiving hitters, Castillo’s increased usage of it is resulting in it being less effective overall. In short, an effective changeup is best utilized alongside effective fastballs, which Castillo has struggled to command.


Let’s move on to his sinker now.

With the sinker, the idea is to induce weak contact. It’s often utilized when a pitcher is trying to create a ground ball. The idea is that a hitter thinks a pitch is coming down the middle of the zone and decides to swing, at the last moment, the baseball dips, resulting in a ground ball. Since the sinker is designed to induce contact, it typically has a lower whiff percentage and higher expected batting average.

So how does Castillo’s sinker hold up?

On paper, it should actually be an above average pitch. He throws it with above average velocity (96 MPH) and it also has an above average vertical drop (25.6 inches, 11% better than average). The problem with this pitch is that when it sinks, it’s sinking to the middle of the strike zone. This has resulted in a 55.6% hard hit rate against this pitch. In spite of this, he’s still inducing ground balls at a 53% rate. However, with the Reds defensive shortcomings and the exit velocity he’s allowing, these ground balls are becoming hits.

Let’s take a look at the movement on his sinker.

We’re starting to notice a trend with Castillo’s pitches. They’re very similar to what he was throwing in 2020, except that they’re dropping more and breaking less. In the case of the sinker, that drop isn’t necessarily a bad thing. It is a sinker, after all. The fact that it is breaking less horizontally means that the pitch is less deceptive to the batter, making it easier to barrel up.

This affects his changeup, too. The sinker helps him set up his changeup because they have similar movement at different velocities. Note how he used both pitches in similar areas of the strike zone last year.

Finally, let’s take a look at his slider.

The slider is a pitch designed to induce a swinging strike. It operates similarly to a curveball, except that it often moves horizontally. Last year, Castillo effectively utilized the slider, dotting the bottom right hand side of the strike zone. 2021 has been a completely different story. Similarly to his fastball and sinker, Castillo has been leaving his slider in the middle of the plate. It’s simply not breaking when he throws it. In fact, his slider’s horizontal movement is 69% worse than average. It’s no wonder that hitters have had so much success against it this year.

Now to examine the slider’s movement.

On average, a slider has about 10 inches of break to it, but Castillo’s slider hardly breaks at all. During the 2020 season, he averaged no horizontal movement. He’s been able to improve this year by two inches, which is still well below average. The lack of horizontal movement isn’t necessarily a bad thing. Many pitchers do this by design, and Castillo was able to be even more effective last year with less movement. What’s happening is that Castillo simply isn’t deceiving hitters anymore. His pitching repertoire, including his slider, is designed to play off his elite fastball velocity.

When you combine a subpar fastball with a slider that is not fooling hitters, and then that slider gets hung over the middle of the plate, you’re asking for trouble.


So what’s wrong with Luis Castillo? The short answer is that he’s consistently throwing hittable pitches in the middle of the zone. They’re not coming in as quickly, and there’s not as much horizontal break, making it easier to barrel up the balls. He’s also not using his fastball to effectively set up his more deceptive pitches. In the past, when he was ace level, those pitches dotted the edges of the strike zone with more horizontal movement. He ended up walking more hitters, but he was also much more effective overall.

Castillo has been an important pitcher for Cincinnati over the past few years and a return to form would provide a major contribution as the Reds push towards the playoffs. If he continues throwing down the middle of the plate, however, batters will continue to hit him hard.

Personally, I believe in Luis Castillo. He’s been my favorite Red to watch over the last few years, and I’m rooting hard for him to be the same guy we’ve gotten used to. He’s been able to work through rough patches in the past, and I’m betting on him to work through this too.

(Photo by Nick Tre. Smith/Icon Sportswire)

Micah is a lifelong Reds fan who grew up watching games at Cinergy Field with his family. A recent MBA graduate, Micah has always had a passion for data analytics and uses his understanding of big data to better understand and appreciate what is happening on the baseball diamond and in the front office. When he's not watching baseball, you can find Micah and his wife frequenting different restaurants and coffee shops in the area. For questions and inquiries, please reach out to

Inline Feedbacks
View all comments
6 months ago

Wonderful article. It was as organized and clearly argued as a brief scientific research paper. “Location, location, location” is very telling. A lot of difference between them, but Cueto was getting hammered when he first went to KC, because Sal Perez was setting a higher target than he was used to. As the “new guy” he didn’t want to say anything about it. Once he did there was immediate improvement.

Micah Greenhill
Micah Greenhill
6 months ago
Reply to  pinson343

Thanks! This article was a lot of work, so I’m glad you enjoyed it.

Great point with Cueto! It’s fascinating how precise pitchers have to be in order to be effective.

Jonathan Andrews
Jonathan Andrews
6 months ago

Thanks for that. It places data to my internal frustration.

Micah Greenhill
Micah Greenhill
6 months ago

It has been frustrating. I hope he figures it out quickly!