Seattle Mariners starting pitcher Luis Castillo demonstrated a notable increase in fastball velocity during his first spring training start, generating buzz within the organization. This improvement follows an intense offseason program aimed at enhancing his performance as the team prepares for the upcoming season.
In Friday night’s game against the Arizona Diamondbacks at Peoria Stadium, Castillo’s fastball velocity nearly matched his 2025 season averages. His four-seam fastball averaged 95 mph over 20 pitches, while his sinker reached 94.9 mph. For Castillo, who is entering his age-33 season, achieving these speeds early in spring training marks a departure from his usual pattern of building velocity gradually as the year progresses.
I think the important thing for me was going out healthy and being able to attack the zone,
Castillo said through an interpreter.
That’s exactly what we saw out there, and I was super happy with what I saw. That was part of some of the training that we did in the offseason.
Adjusted Offseason Strategy Aims to Sustain Velocity
Historically, Castillo’s fastball velocity tends to increase incrementally throughout the season, but after a late-season decrease in 2025 and entering the prime age of 33, he shifted focus during the offseason. He emphasized maintaining his pitching velocity across the full campaign rather than peaking later.
Castillo’s 2025 season concluded with inconsistent stretches, including a difficult period from August to September when his earned run average ballooned to 10.06. His briefest outing as a Mariner occurred in Game 4 of the American League Championship Series, lasting only 2⅓ innings.
Very long training, Castillo described regarding his offseason routine, withholding further specifics for later discussion.
We tried to increase the velocity, but yeah, we worked a lot on it.
Enhanced Cardiovascular Workouts Yield Early Benefits
Central to Castillo’s improved velocity is a heightened emphasis on cardiovascular conditioning. Known for running stadium stairs during the regular season to maintain endurance, he substantially increased his mileage in the offseason, pushing beyond his usual limits.
I think I ran 15 or 20 more miles than what I’m normally used to,
Castillo revealed.
This uptick in cardio training is intended to help Castillo sustain higher velocity deeper into games and later in the season, addressing the endurance challenges he faced previously.
Although Castillo’s spring debut line included three earned runs over 1⅓ innings, fastball velocity and command are considered more critical indicators during spring training. By comparison, his fastball velocity last spring training began at an average of just 93.9 mph.
Potential Leadership Role in Mariners’ Pitching Rotation
The timing of Castillo’s velocity increase supports Seattle’s aspirations, as the Mariners position themselves as a serious contender. Alongside emerging ace Bryan Woo and established starters Logan Gilbert and George Kirby, Castillo’s resurgence could provide vital veteran stability and depth to the pitching staff.
Castillo’s renewed conditioning regimen not only reflects physical improvement but also signals his commitment to maintaining high performance throughout the season. This determination aligns with the team’s goal of making a deep playoff push.
The encouraging spring results suggest Castillo’s offseason efforts are already influencing his game positively. If he sustains this velocity and avoids the late-season performance decline that troubled him in 2025, Castillo may help fill a key role in Seattle’s pursuit of a championship.
