In 2019, Luis Castillo stopped throwing strikes. Pitchers around baseball are always introducing subtle changes in the way they approach things on the mound, tweaking anything from their mechanics to their pitch mix or adding a tick of velocity. But Castillo’s adjustment was not subtle. Over his first two big league seasons, he’d had just one month in which he threw fewer than 49% of his pitches in the strike zone, and that was the first month of his career. Then, in the first month of 2019, just 40.3% of his pitches finished in the strike zone. The next month, that went down to 37.1%. He finished the year having thrown the fewest strikes of any qualified starter in baseball.
The suddenness of Castillo’s dip in strike-throwing made it seem likely the change was intentional, and if it was, it was a success. Sure, Castillo posted the highest walk rate of his career, but he also set a new career-best in strikeout rate, while also turning in far and away the best season of his career in terms of WAR. The 27-year-old right-hander and the Reds must have seen more correlation than causation between Castillo’s zone rate and his overall performance, however, because to this point in 2020, he’s gone right back to throwing strikes again.
Castillo was a bit of a curiosity when he was acquired by the Reds as the return for sending Dan Straily to the Miami Marlins before the 2017 season. He was one of the harder-throwing starting pitchers in the minors, sitting in the mid-to-high-90s and capable of flashing triple digits, but didn’t have the control problems that can often arise when someone is trying to corral such a high velocity. In 131.2 innings between Advanced-A and Double-A in 2016, Castillo walked just 25 hitters against 103 strikeouts, an enticing set of numbers for a Reds team that just happened to suffer the highest walk rate in baseball at the major league level that year.
Notice I said “curiosity,” though, and not “ace in waiting.” As interesting as a pitcher who can consistently throw 98-100 mph for strikes is, he needs to actually miss bats in order to have a high ceiling in the majors. Before being traded to Cincinnati, Castillo hadn’t shown he could do that yet, and his stock reflected as much — FanGraphs’ Eric Longenhagen rated him as the Reds’ 10th-best prospect after the deal, theorizing that he was likely a No. 4 or 5 starter. Getting Castillo to the level he’s at now — a 4-WAR starting pitcher who can run some of the highest strikeout and groundball rates in the majors — has been a long process including tons of adjustments.
The biggest of those adjustments in 2019 was Castillo leaning on his changeup like the game-breaking weapon it is — he threw it 32.5% of the time last year, more than any of his other pitches — but the emphasis on missing the zone more often wasn’t far behind. Each pitch saw a similar decrease in zone rate last year, and each one has seen an almost identical uptick this year.
If the dramatic decline in strikes coincided with such a strong performance for the season, why reverse course? Well, for one thing, Castillo is not a pitcher who needs to miss the zone in order to achieve swings and misses. He was one of only six qualified starters who held opponents to in-zone contact rates under 80% last year, with Gerrit Cole, Lucas Giolito, Justin Verlander, Max Scherzer and Robbie Ray making up the rest of the group. That’s some elite company to keep, and with the exception of Ray, everyone else had a zone rate at least nine points higher than Castillo. Being able to get whiffs on pitches that would be called strikes regardless of what decision the batter makes is a huge leg up for any pitcher, one that diminishes the necessity for a pitcher to venture outside the zone. Castillo appears to be taking that lesson to heart in 2020 and if you look at the leaderboards for which starters have the lowest in-zone contact rates this season, guess who happens to be at the top:
Lowest Z-Contact% in 2020, min. 20 IP
We’re still talking about only a handful of starts for everyone, but by and large, these are the names one expects to see at the top of this list. We’ve always known that Castillo had the ability to throws lots of strikes — the only question was whether doing so made him the most effective pitcher he could be. Now that he’s the most unhittable starter in baseball inside the strike zone, that poses a real headache for hitters.
Even more important for Castillo is that he’s throwing strikes when they’re most important. Last season, he started just 56.3% of plate appearances with a first-pitch strike, the fourth-lowest figure among all qualified starters. That meant that even though Castillo was working with some of the most dominant stuff in the game, he was allowing batters to dictate the direction of any given at-bat from the very beginning. With a rekindled interest in throwing strikes this season, Castillo’s first pitch strike rate is the 11th-highest in baseball. Only Jon Lester has made a bigger improvement in the way he opens at-bats.
Biggest gains in F-Strike%, 2019-20
|Name||2019 F-Strike%||2020 F-Strike%||Change|
|Name||2019 F-Strike%||2020 F-Strike%||Change|
It’s easy to forget that the Castillo we see before us, with his triple-digit heat and viral-GIF-ready movement on all of his pitches, didn’t always look this way. Look at what was written about him before the 2017 season, and his changeup is an afterthought or not mentioned at all. Even his slider — which has resulted in a .063 wOBA from hitters this year and a 41.7% whiff rate — is still sometimes thought of as a work-in-progress. Castillo is undoubtedly one of the most talented pitchers in the sport, but he’s also the product of a ton of hard work, both on his part and those who have worked with him along the way. That work is ongoing, the adjustments still being sorted out, all in an effort to inch closer to what the right-hander’s full potential really is.