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How Willi Castro Made the Most of a New Opportunity

More patience in one area, more aggression in another

Division Series - Houston Astros v Minnesota Twins - Game Three Photo by David Berding/Getty Images

When the Detroit Tigers declined to offer the arbitration-eligible Willi Castro a contract after the 2022 season, it qualified as a mild surprise. While Castro was coming off his second-consecutive disappointing season, he was still just 25 years old, not far removed from being one of the Tigers’ top 10 prospects and a tied for 4th-place American League Rookie of the Year finish in 2020. He was projected to be owed $1.7 million in arbitration, a non-trivial amount of money for a rebuilding club, but not enough to make him an obvious non-tender candidate.

The Twins were in the market for middle infield and utility player depth – this was before they landed Carlos Correa in free agency and Royce Lewis was still rehabbing a second torn ACL – when Castro hit the market as a free agent. In four seasons with Detroit, Castro made 108 appearances at second base, 92 at shortstop, 93 in the outfield, and a handful at third base. Minnesota quickly scooped him up on a minor-league deal.

When in Doubt, Swing

As a prospect, the report on Castro was that he was a versatile switch-hitter with some natural power he hadn’t quite figured out how to get to in games. He was seen as a solid defender at second and third base, and someone you could deploy at shortstop in a pinch. FanGraphs limited his ceiling to the borderline between utility man and low-end regular due to his free-swinging approach at the plate.

The lack of plate discipline and patience was evident in the Majors from the beginning, as you can see from this table of seasonal plate discipline metrics:

Data from Baseball Savant

Castro swung at an uber-aggressive 54% of the pitches he saw (compared to the 47.1% league average during the Statcast era) in his 2019 debut.

That aggressiveness ticked up yearly until it reached 58.2% in 2022 – the 10th-highest swing rate among the 285 players to take 250 plate appearances or more that season. That aggression was paired with increasing contact rates year over year.

Curiously, despite the uptick in swing rate, Castro’s chase rate held pretty steady at just under 40% throughout that period. He swung more often, but not at pitches out of the zone. Instead, a lot of those swings came against pitches in the shadow zone around the edges of the plate. The percentage of pitches to Castro in the shadow zone that he swung against increased steadily each season:

Swing Rate in Shadow Zone:

  • 2019: 57.1%
  • 2020: 63.0%
  • 2021: 64.9%
  • 2022: 67.8%

Unfortunately, that combination also meant that Castro was frequently putting the ball in play in sub-optimal ways. Aggregating all the hitters to take at least 500 plate appearances from 2019 through 2022, Castro’s combination of swing rate and exit velocity was one of the worst in the league:

Data from Baseball Savant

Castro posted just a 64 wRC+ in his 30-game 2019 cup of coffee. An exciting 154 mark followed that in the shortened 2020, but in hindsight, it was fueled in some significant measure by a .448 batting average on balls in play (BABIP). The league average was .292 that season. Castro’s production, and his BABIP, plummeted back to Earth in 2021 (69 wRC+, .275 BABIP) and 2022 (84 wRC+, .288 BABIP).

Castro’s approach to swing his way out of his struggles wasn’t working. The data tells a classic story of a young player trying to do too much.

Another Approach in Minnesota

In Spring Training before the 2023 season with the Twins, Castro was far from a guarantee to get a roster spot, but he knew then what needed to change. “Just being patient,” Castro said to Do-Hyoung Park. “Sometimes, as a player — not just me, but every player — sometimes, you try to do more than what you’ve got to do, and that’s the stuff I’ve been focusing on. I know when I’m there, just settling down, getting a good pitch to hit, everything just comes out natural.”

Castro made good on that pledge and had the best season of his career. Over 409 PAs for Minnesota last season, Castro competently played every position but first base and catcher, hit .257/.339/.411 (109 wRC+, .328 BABIP), and finished 3rd among the team’s position players in bWAR (2.7) and 4th in fWAR (2.5).

While he benefitted a bit from friendlier batted ball fortune, he also meaningfully improved his approach at the plate. He toned down his aggression and reduced his overall swing rate to a career-low 51.6%. That helped his chase rate drop by more than five points to 34.6%.

Castro also became more selective in and around the strike zone. His swing rate against pitches Statcast mapped inside the strike zone dropped from 77.2% to 69.0% and his swing rate against pitches in the shadow zone dropped about thirteen points to 54.9%.

At the same time, Castro’s contact and whiff rates both improved slightly.

All of that helped Castro hit the ball harder and take his walks in ways that he never had before. His 86.5 mph average exit velocity, 114.2 mph maximum exit velocity, and 8.3% walk rate were all career bests and helped to raise the floor of his profile at the plate.

More Aggressive in Another Area

While Castro was toning down his aggression at the plate, he was amping up his aggression on the base paths. Part of the appeal of Castro as a prospect was his above-average speed and ability to run the bases. He swiped more than 15 bases at each level on his way up the minor league ladder. In his four seasons in Detroit, that part of his game didn’t seem to translate to the highest level.

He didn’t steal his first base as a Tiger until 2021 (his third MLB season) and was just 18 of 28 combined on stolen base attempts in his Tiger career, despite ranking in the top ~15-20% in running speed (by Statcast) each season.

MLB instituted rule changes before last season to incentivize stolen bases and Castro took advantage in swiping 33 bases in 38 attempts just last season (including three thefts of home). That mark easily led the club and ranked 10th in MLB.

MLB: SEP 06 Twins at Guardians
Minnesota Twins left fielder Willi Castro (50) is safe at second with a stolen base
Photo by Frank Jansky/Icon Sportswire via Getty Images

Baseball-Reference tracks stolen base opportunities as plate appearances where a runner is on 1st or 2nd base with the next base open. Castro had 158 such opportunities last season and he attempted to steal in 38, or 24%, of them. That rate was triple his 8-9% marks from 2022 and 2021, in roughly similar numbers of opportunities.

In the same kind of fashion, Statcast tracks non-stolen-base baserunning advances, like going first to third on a single. Castro had 84 chances last season and went for them 44% of the time, which was about seven points more than in 2022 and five points above 2021.

Altogether, FanGraphs measured Castro as providing 6.4 runs above average with his baserunning last season, which was quadruple his career total from Detroit.

Conclusion

To close this out, I want to be clear that these adjustments don’t fundamentally change the type of offensive player that Castro is. He is not a patient, selective hitter. He’s still an aggressive free-swinger. That’s evidenced by the fact that his swing rate last season, while toned down from before, was tied for the 67th-highest among the 294 players to take 250 plate appearances last season. His chase rate was still well above the 28.6% league average.

That those marks were significantly less extreme than they were before gives him a better chance to be productive at the plate in addition to the floor he brings defensively and on the bases. It’s a perfectly cromulent combination of value for a utility player.

His maximum exit velocity data, and his prospect scouting report, suggest he might still have another gear in the power department, but he’ll need to maintain (or better yet, improve further) his discipline and selectivity to get to it.

Absent that, like another multi-positional, fast, switch-hitting former Twin (Danny Santana), Castro will continue to be overly subject to the vagaries of batted ball luck at the plate and will have to lean on his defense and baserunning to contribute.


John is a writer for Twinkie Town and Pitcher List with an emphasis on analysis. He is a lifelong Twins fan and former college pitcher. You can follow him on Twitter @JohnFoley_21.