Diego Castillo is a key to the Rays bullpen against the Astros

Diego Castillo broke into the majors in 2018 with a very good season. He put up a 3.11 ERA/3.30 FIP/3.38 xFIP in 56.2 innings. His 29.3% strikeout rate set him up to be an important cog for the Tampa Bay Rays bullpen over the next few years, and he was also a versatile one.

Castillo was asked to to get anywhere from 3 to 6 outs and was the second most used opener with 11.

The 2019 Season

In his follow up season, most of Castillo’s peripherals stayed roughly the same:

• His strikeout rate fell 1.4% to 27.9%.
• His walk rate rose 0.9% to 9.0%.
• He allowed a few more homers (1.05 HR/9 compared to 0.95 HR/9 in 2018).

The one big change was that his groundball rate increased 11.6% to 56.9% in 2019, and his BABIP spiked from an unsustainable .229 to a more believable .300.

Overall his 3.41 ERA/3.72 FIP/3.72 xFIP looks much worse than what he put up in 2018, but remember that offense spiked in 2019, and that home runs are flying out of ballparks. In the context of the league, both seasons he put up a 77 ERA- and his FIP- increased only marginally from 81 to 84. He’s been basically just as productive.

But despite those similar numbers Castillo’s season has felt disappointing, and that has to do with which moments we fans remember.

Castillo got off to a good start through the first two months of the season with a 2.15 ERA/3.66 FIP/3.96 xFIP through 29.1 innings. Then came a dreadful June. He only made 6 appearances and threw 5.0 innings, but he put up a 14.40 ERA/9.81 FIP/6.21 xFIP in those innings.

His two late-inning meltdowns against the Athletics were a big part of the reason the wild card game was played in Oakland.

On June 23 Castillo went on the injured list due to right shoulder discomfort and would return three weeks on July 12 as the team got back to the grind following the all-star break.

Since returning from the injured list Castillo has been dominant. In 34.1 innings he’s put up a 2.88 ERA/2.89 FIP/3.15 xFIP. That’s good for a 65 ERA- and 66 FIP-. His strikeout rate has improved to 30.1% and his walk rate has fallen to 7.0%.

Castillo has been everything the Rays could have expected since returning, and in the Wild Card Game against the Athletics the Rays showed their faith in him and were rewarded. Castillo was the first man out of the bullpen, and he threw two scoreless innings, picking up three strikeouts. He provided the bridge to Nick Anderson and Emilio Pagan to close out the final two frames.

Castillo’s Pitch Usage

At his core Castillo is a two-pitch pitcher. He throws close to a 50/50 mix of fastballs and sliders.

Castillo throws two fastballs. Both come in averaging around 98.5 mph. His fourseamer (12% usage) gets about three inches more glove side movement than the sinker, and gets about two inches less drop. Visually, it acts like a cutter in that it doesn’t get much movement, but has enough to keep it off the barrel, because batters are attuned to his more used two-seam fastball. Batters have whiffed on 14% of his fourseamers.

Castillo’s second fastball is a sinker that he throws 36% of the time. The pitch has noticeable armside run, and drops in comparison to his fourseamer. Batters whiffed on 8% of his sinkers, and hit over 60% of the balls in play against it on the ground.

Castillo’s breaking ball is his putaway pitch. Depending on who you ask it either is a slider, curve, cutter, or just a “breaking ball.” The pitch comes in around 89 mph. It has a foot of glove side run compared to his fourseamer and six inches of additional drop. Combined with a ten mile per hour differential and you get a 20% swinging strike rate. tldr, it’s nasty.

Right handed batters hit .205/.295/.342 and put up a .277 wOBA against Castillo in 2019. Left handed batters have fared much better with a .271/.340/.427 line and .318 wOBA.

In his matchup against the Athletics on Wednesday night he leaned on his slider. 21 of his 33 pitches were sliders including picking up swinging strikes on two strikeouts.

But what role for the playoffs?

The bulk of the threats in the Astros lineup are right handed (he will have to be most careful against lefties Michael Brantley and Yordan Alvarez), which makes him one of the best Rays options out of the bullpen, so the question for manager Kevin Cash is how to use him over the course of the series?

It’s uncommon for Castillo to pitch in back to back days, but he did appear in five of the six games in the run down the stretch against the Boston Red Sox and New York Yankees, so he’s definitely able to.

But using his multi-inning ability today would probably take him out of the game tomorrow. The choice will likely be either throwing him for one inning in back-to-back games, or to get six outs in one of the games.

Can Cash afford to use Castillo for two innings today? Can he afford not to?