Miguel Castro’s 2019 slump may have just been growing pains

A couple of weeks ago, our Drew Bonifant defied the haters and predicted Orioles reliever Miguel Castro would have a bounce-back 2020 after finishing the 2019 season with a disappointing 1-3 record and a 4.66 ERA. As Drew ably demonstrated, Castro’s ERA and win/loss record gave a false impression about a season in which pretty much all of his other indicators improved: batting average against, WHIP, walk rate, and most gaudily, strikeout rate (from 5.2 in 2017 to 5.9 in 2018 to 8.7 in 2019, a huge jump).

In fact, besides ERA, Castro’s only major indicator that worsened was home runs against. Drew’s conclusion: the Orioles’ 6’7” fireballer was missing inside the zone, and his mistakes were getting hit up harder. He’s right. But there’s even more to say about what Castro has been up to behind the scenes.

First, Castro’s performance needs to be put in the context of a season where all MLB pitchers combined for the highest number of home runs allowed in modern baseball history, as well as the seventh-worst ERA (6,776 and 4.51, respectively). So it’s clear that whatever bug Castro caught in 2019 was one afflicting a whole heckuva lot of other pitchers, too. (Here at Camden Chat, we’ve written about the juiced ball before, but if you’re curious, it’s very well-covered here and here and here.)

There was another important thing that was different for Miguel Castro in 2019: it was his first season under the new regime of Mike Elias & Co. Did the new analytics-informed coaches make tweaks to Castro’s stuff? You bet they did!

One obvious area is in pitch arsenal. As you can see below, not only did Castro finally get rid of his four-seam fastball, a pitch he’d been phasing out since 2016, but he also upped his offspeed usage. In 2018, Castro threw his sinking fastball 58.5% of the time, the slider 26.2% and the changeup 15.2%. In 2019, meanwhile, Castro went to the heat less than half of the time (48.9%), alongside a more frequent slider (31.1%) and changeup (20%).

The new regime has also drawn out of Castro appreciable improvements in velocity. As a 20-year-old whippersnapper, Castro averaged about 97 mph on his four-seam fastball, which he used about twice as much as his other pitches. Now, as he’s subbed out that flatter fastball for one with some sink and reduced his dependence on heat in general, his velocity has ticked back up to 97.3 mph (up significantly from 95.4 mph in 2018). The 7-10 mph separation between that pitch and the changeup and slider are still enough to keep hitters off-balance.

Vertical break is another area of improvement you can credit to the new regime. Since 2018, Castro has radically retooled his slider and changeup, adding almost 2 inches of drop to the first, and about 3 inches to the second.

Castro’s spin rates keep ticking up, too. At 2,287 RPM, his fastball spin would be merely pedestrian, except that, thrown at 97 mph, it becomes an above-average weapon. His slider also clocks in at an insane 3,029 RPM (although, as that same post explains, there are so many different pitches called “sliders,” it’s hard to compare them without making your head explode). Interestingly, although a recent FiveThirtyEight article ranks the 2015-18 Orioles as one of the league’s least spin rate-conscious teams, Castro’s upward trend in spin rate dates back to even before the 2017 season.

Finally, here is some great data on Castro’s pitch arsenal from Baseball Savant. As measured by expected weighted on-base average (xwOBA, see below, useful primer here), all three of Castro’s pitches were of a higher quality in 2019. (The whiff rate also increased on Castro’s offspeed stuff, although it went down slightly on the fastball).

So what about Castro’s struggles with the long ball in 2019? Well, Castro gave up 10 home runs over 70 innings—seven off of the fastball, two off of the slider, and one off of the changeup. Overall, last season he allowed fewer barreled balls, except on the slider. His hard-hit percentage increased a bit off the fastball and the slider, as did exit velocity off the fastball, but just a tick. Interestingly enough, average launch angle went down for Castro across all pitches.

What all this suggests is that Castro’s long balls aren’t the result of weak stuff, but rather—just as Drew guessed—mistakes in the zone. If you look at Castro’s Statcast Zone charts below, showing home runs and xwOBA per hitting zone, these are probably mistakes of two varieties: one, hanging sliders, a pitch he’s still developing, and fastballs down-and-in to right-handers.

My guess is, under the Elias regime, the coaches have pointed out the fact that major league hitters are better fastball hitters than ever, so that even an above-average fastball is more effective when used to set up offspeed stuff. This is consistent with league-wide best pitching practices: fastballs are in fact getting faster at the same time as they’re getting rarer.

So while the notoriously hard-to-harness Castro will continue to lob a few mistakes over the plate now and then, this team rightly has faith in their hard-throwing righty. Judging from the numbers, it seems like the work is starting to pay off.