The Seattle Mariners pitching staff was one of the tumultuous parts of what was an overall incredible season.

Despite being closer to the World Series than ever before in franchise history, the starting rotation was in an almost constant state of flux.

Four of the five pitchers on the rotation missed time with respective injuries. The only pitcher that wasn't was the eldest — three-time All-Star Luis Castillo.

With the chaos that was the starting rotation, Castillo's steadiness was something that provided the team much-needed reprieve. But even Castillo's veteran arm wasn't immune to hiccups.

Luis Castillo by the numbers

Games played: 32

Pitching stats: 3.54 ERA, 11-8 Record, 180.2 IP, 162 SOs, 1.18 WHIP, .244 Opp. BA.

What I liked

Castillo's consistency was his biggest strength but that goes beyond just this season.

For the third year in a row, Castillo posted 18 quality starts. He had a sub-4.00 ERA for the seventh-straight year.

Castillo's fastball also remained solid despite it not having the upper-90s velocity typical for the 32-year-old.

Castillo's fastball had an average velocity of 94.9 mph, according to Baseball Savant. In 2023, he averaged 96.3 mph. In 2024, he averaged 95.6 mph.

Even with the drop in velocity, opponents averaged .200 against Castillo's four-seam fastball and he generated a whiff rate of 26.5% with the offering. He had a fastball run value of 11, which ranked in the 90th percentile of baseball.

Castillo didn't have as much luck with the other pitches in his repertoire. Opponents averaged .310, .230 and .294 against his sinker, slider and changeup, respectively. But his fastball was good enough to be utilized as a building block to his outings and as a last-resort when he needed it.

Best games

As the season went on and Castillo received more questions from media on how his arm was feeling, he reaffirmed how strong he was feeling.

Castillo proved that statement with his final outing of the regular season against the Colorado Rockies on Sept. 24.

Castillo fanned a season-high 10 and allowed one earned run on one hit (one home run) in 7.1 innings pitched. It was the first time he struck out double-digit batters since a showing against the Minnesota Twins on July 19, 2023.

Future prospects

There might not be a player on the team that has been involved in more trade rumors than Castillo over the last year. He's set to earn a $24.15 million salary in 2026, which is the final of a five-year, $108 contract extension he signed with the Mariners after being acquired in a trade with the Cincinnati Reds in 2022.

Castillo's deal included a full no-trade clause from 2023-25 and a $25 million vesting option for 2027 that kicks in if he reached 180 innings pitched. If he were to miss more than 130 days with a UCL injury, that vesting option becomes a $5 million team option.

There were rumors floated around last year during MLB winter meetings that Seattle and the Boston Red Sox were discussing a trade that would have sent Castillo out east in return for first baseman Triston Casas.

That deal ultimately didn't happen and the Mariners found their first baseman of the future in the form of 2025 trade deadline acquisition Josh Naylor, who signed a five-year, $92.5 million contract earlier this month.

Due to Castillo's age, owed salary and contract status, he'll likely be tied to trade rumors until the deadline passes or a move is made. But he's still an important part of the rotation, as he proved this year.

Final grade: B

Beyond his end-of-season numbers, Castillo was also consistent when looking at his month-to-month numbers.

Castillo had a sub-4.00 ERA in every full month of the season except for one. He had a 3.62 ERA in April, a 3.00 ERA in May, a 3.97 ERA in June, a 2.05 ERA in July and a 2.45 ERA in September. The only month he posted an ERA above 4.00 was in August, where he posted a 6.66 ERA.

In the playoffs, sans Bryan Woo, Castillo had a 3.24 ERA and fanned five batters in 8.1 innings across three appearances (two starts).

Castillo likely won't have a Cy Young consideration in his future, but he's still a solid No. 2 or No. 3 starter on a championship-caliber team. He earned the nickname "the rock" for a reason. And being solid as one is why he earns a "B" for his 2025.

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