2021 Arizona Diamondbacks Reviews, #24: Humberto Castellanos

• Rating: 4.25
• Age: Turned 23 on April 23.
• 2021 Stats: 14 G, 7 GS, 45.2 IP, 48 H, 26 R, 25 ER, 7 HR, 15 BB, 29 SO, 4.93 ERA, 5.01 FIP, 0.3 bWAR
• 2021 Earnings: league minimum
• 2022 Status: Pre-arb, on 40-man roster, one minor-league option left

Humberto Castellanos is a name that may or may not ring bells for most of us, but for the 2021 Diamondbacks he was an emergency call up that supplied essentially replacement level value in a reliever/emergency starter role. That’s not a description that necessarily inspires hope on the surface, but a deeper dive into the context of his career and Statcast numbers shows many reasons for optimism (at least for those of us that have huffed enough Copium).

Signed during the 2015 J2 Period out of Mexico by the Astros at 17 years-old, Castellanos began his professional career as a SP in 2016. He showed some promising peripherals, but his strikeout numbers were not among them. It seems that in an effort to compensate for the swing-and-miss deficit, the Astros converted him to a relief role (one he occupied until being acquired off of waivers by the D-Backs). The job switch did bring his K numbers to more acceptable levels, but they were never exceptional in larger sample sizes. In spite of the lackluster K numbers, a combination of a GB% that hovered around 45% and a BB% that didn’t exceed 6% until reaching AAA earned him a call to MLB during the 2020 season.

In a little over ten innings he struggled to get swings-and-misses and to throw strikes with his usual consistency, which left him with slightly below replacement value production and non-tendered at the end of the year. After being acquired by the D-Backs, he was immediately converted back to a SP and sent to Reno. Even though he was making his first starts since Rookie ball, he showed enough to again earn a call to the Majors and put up slightly above replacement level value this time. However, the numbers put up don’t make for a very exciting story; “23 Year-Old Rookie Struggles in Major Leagues”, in other news, “Water is Wet”. The most interesting part of his season is quite possibly the shift in his pitch characteristics and usage (or the difference in organizational pitching philosophies if you’re feeling a little more meta).

We’ll be looking at Baseball Savant’s movement and spin direction tables; movement is quite literally the vertical/horizontal movement and spin direction is quite literally direction of spin. A 4-seam fastball with 1:30 spin direction (read as 1 hour 30 minutes, where each hour is 30 degree increments of a circle and each minute is a further breakdown of each hour into four quarters) will rotate in that direction from the batter’s viewpoint. There are two types that are measured, Spin-Based and Observed. Spin-Based is the spin that’s seen by the batter, while Observed is based on the final movement (or theoretically the angle that would produce that movement). Now that that explanation is out of the way let’s look at the individual pitches, starting with the most used and ending with the most effective.

In Castelllanos’s D-Backs tenure he’s worked primarily off of his sinker. Compared to his Astros cameo the sinker has the same Spin-Based and Observed movements (1:45 and 2:45, respectively); while it has fractionally less vertical/horizontal movement, it’s velocity has also increased by a little more than 1 mph.

The 4-seam fastball has the same Spin-Based movement from last season at 1:30, but the Observed movement has deviated an extra 15 minutes to 1:00. The vertical movement has stayed essentially the same and the horizontal movement has dropped by about 2.5 inches. There was also a small velocity increase, making the the 4-seam and the sinker incredibly similar in speed (90.4 mph compared to 90.5 mph) while coming out with incredibly similar spin and a larger horizontal separation.

The slider is a bit less straightforward, having shifted the spin direction further away from the two fastballs (from 1:15 to 12:45) and sacrificing a little under one inch of vertical movement to gain slightly more than one inch of horizontal movement. The most confusing part of the whole slider profile is that the pitch actually gained almost half a tick on the radar gun but also technically has more movement overall. Natural velocity gain is one explanation, but there’s also the outside possibility of attempts at throwing a cutter. The latter is purely a theory, but it’s something worth keeping an eye on.

The changeup is another pitch that had a small shift in spin direction from 2:15 to 2:00, making the spin much more similar to that of his Sinker. The horizontal movement on the cambio is identical to last season, but there was about 3.5 inches of vertical movement sacrificed for a velocity gain of 1.3 mph. Not necessarily what we’re looking for, but maybe it’ll sound better when we bring in the curveball.

Speaking of the curve, we’ll have to introduce a concept called Spin Mirroring. It’s really simple, any two pitches that are separated by exactly 6 hours of spin direction are said to “spin mirror” because they’re rotating in the exact opposite direction from each other, so even if a hitter can pick up on the axis of spin they can’t tell if it’s going forward or backward. His curve went from perfectly mirroring his changeup last season to.... perfectly mirroring his changeup this season (shifting from 8:15 to 8:00). This is significant because his change is looking more like his sinker, therefore his curve more closely resembles his sinker as well.

Combine this with a vertical movement increase just shy of seven inches, a horizontal movement increase just shy of 3.5 inches, and a drop in velocity of about 2 mph and we’re left with larger differentials between his curve and every single other pitch (the most stark change being the 4.5 mph curve/change separation becoming 7.9 mph, although the 14.2 mph sinker/curve separation is pretty nice). The added fact that his curve breaks in the opposite direction from every other pitch (sans the slider) adds even more for batters to consider, the curve’s .181 xwOBA doesn’t seem particularly flukey.

Changes in pitch behavior lend themselves to changes in pitch usage; it’s not really surprising that with two pitches playing better off of his sinker that he’d switch over to using it as his primary fastball. However, that statement is only partially true; his 2020 approach was akin to the kitchen sink for everybody. The 2021 season featured a similar approach against lefties, but he was almost entirely sinker/curve against righties. This new approach combined with his ability to fill the zone saw less swings on pitches in the zone, more called strikes (enough to offset his lost swinging strikes), and more soft contact. Although it’s yet to be determined whether soft contact is a repeatable skill of his, underlying numbers suggest that batters were struggling to read his pitches (interestingly BaseballSavant suggests the closest pitcher by batted ball metrics to Humberto Castellanos was Tyler Gilbert, it’s recommended that you check his spin direction numbers out as well to see why he might not be entirely smoke and mirrors).

All of those qualities are incremental progress toward a more sustainable (if unorthodox) profile; however, it would be cruel to get everyone’s hopes high without going back to point out that he has just began starting games again. As such his highest season workload was last season, and even then it was only a small bit over 100 IP (so we shouldn’t expect much more than ~130 IP next season). Still, this is a soon to be 24 year-old strike-thrower with pitches that at least have the potential to be tunneled to great effect. That’s before considering that he held his own in MLB while undergoing a change in role and repertoire, making Humberto Castellanos one of the more intriguing rotation candidates when Spring Training rolls around (at least in the eyes of the author).