If you entered this season thinking the Cincinnati Reds had a decent shot at winning their division, a big reason for that was probably the starting rotation. And if you thought the Reds’ starting rotation was good enough to carry them to a division title, a big reason for that was probably Luis Castillo. Now 28, Castillo has impressed ever since his debut in 2017, and he’d been one of the best pitchers in the National League not named Jacob deGrom over the past two seasons. From 2019-20, he ranked fourth in the NL in fWAR, sixth in FIP, eighth in ERA, sixth in strikeout percentage, and first in ground ball rate. He’s one of the most talented throwers in the game, and has always seemed to hint at having something extra in the tank.
Unfortunately, if you’re a Reds fan disappointed with the way the 2021 season has gone, a big reason for that is probably also Castillo. Through eight starts, he has the worst ERA in baseball at 7.71, and the next-worst qualified starter is nearly two runs ahead of him. He faced an uphill battle with his ERA beginning with Opening Day, when he gave up eight earned runs before leaving in the fourth inning. He looked much more like his old self in his second start, throwing seven shutout innings against the Pirates. But in the six games that followed, he’s allowed at least three runs in all of them, at least four runs in four of them, and another eight-run outburst in his most recent start against the Rockies. It’s the worst stretch of Castillo’s career by a wide margin.
There’s still time for Castillo to recover enough that his numbers become respectable by season’s end. If he makes 24 more starts this season, averages five innings per game, and pitches at an ERA close to his career mark prior to this year (3.62), he could still finish with an overall ERA of about 4.00. That’s well within the realm of possibility. As you can see in his chart above, his FIP has climbed just like his ERA this season, but not nearly to the same extent. His xFIP, meanwhile, is only around 4.26, which is just a few ticks above league average. Castillo is far from a lost cause, and if you speak to him and those who watch him most, everyone is adamant that he is “close.” Even if that’s the case, though, he hasn’t gotten there yet. And that makes answering the question of what’s causing his struggles an urgent matter.
But it isn’t easy. From a pure stuff standpoint, Castillo is as impressive as ever. His average four-seamer velocity of 96.2 mph is a full tick down from last year, but is pretty much right where he was in 2019, and is steadily increasing as the season goes on — his three hardest fastball averages this year have all come in the last three games. Meanwhile, his spin rates are mostly up across the board, and his pitches are moving about the same amount they were last year or even a tad more. This is all encouraging news. It shows Castillo probably isn’t hurt, nor should his problems be due to his physical gifts prematurely eroding.
You also can’t simply chalk Castillo’s results up to factors outside his control. Usually, when you see a large gap between a pitcher’s ERA and his FIP, batted ball luck is playing some kind of role. When it comes to Castillo, that’s certainly the case — his opponents’ .380 BABIP is far and away the highest in baseball. That should begin to rebound at some point. The Reds have a bad enough defense that pitchers can probably expect to take some kind of hit on balls in play throughout the year, but it isn’t as bad as we might have expected, and nowhere near the worst in baseball.
The thing about Castillo, though, is that balls in play are supposed to be a pretty minimal factor in the first place. He typically has astronomical strikeout and ground ball rates, which means that batters are not only putting the ball in play against him at a below-average rate, but also hitting the least productive kind of batted ball when they do. Even when Castillo has struggled in the past, he’s usually still been able to perform well in these regards — he’s just walked too many hitters in the process. This year, though, his ground ball rate is down more than seven points from last season, while his bat-missing ability has completely disappeared.
When a pitcher’s strikeout percentage falls off a cliff, there are a few obvious places to look. Usually, there’s a red flag in someone’s stuff, but we’ve already determined that shouldn’t be an issue here. It could also be the result of bad strategy when it comes to pitch selection — a pitcher could be holding back too much on throwing his best swing-and-miss stuff, or using too many two-seamers instead of four-seamers. None of that applies to Castillo either. He’s throwing his best pitch, the changeup, more than he ever has. He’s also throwing fewer sinkers than he has since 2017, choosing the four-seamer much more often.
Finally, we can look at his pitch location, but there isn’t a lot of super convincing information here, either. Pitchers can cost themselves whiffs by throwing a ton of pitches in the strike zone, where the batter has the best chance at making contact. They can also hurt themselves by falling behind too often, which reduces the chance they’ll get batters to chase balls out of the zone. Castillo, though, is throwing his second-lowest rate of strikes ever (39%), yet is also throwing from behind in the count at the lowest rate of his career by several points (21.3%), and is provoking his highest-ever chase rate (36.8%). One problem: Before 2021, hitters had a contact rate of just 54.2% against Castillo when chasing a pitch outside the strike zone. This year, that rate is up to 70.6%. It’s a crisis that affects everything he throws.
So much of Castillo’s process seems to say he’s doing things the right way, and his stuff looks like it should be as dominant as ever. And yet, the results are what they are. The suddenness and magnitude of Castillo’s struggles suggest an obvious cause, but if it can be found somewhere in his numbers, it’s eluded me for weeks. My hunch is that the cause is obvious, and that it’s just something that doesn’t show up in any data: Tipping pitches. It could explain the out-of-nowhere ability for hitters to make lots of contact, despite Castillo being in advantageous counts and throwing with the same velocity and movement to the same locations he always has. I’m not certain of that by any means, though — it could also be a combination of lots of minor factors and some small sample funkiness. As awful as it has felt to watch Castillo’s starts this season, it is mildly encouraging that obvious red flags are so hard to find. Hopefully, that means a return to normal is just as within reach as his teammates and coaches say it is.