Mariners Make Massive Season-Altering Pitching Adjustment In Postseason

The Seattle Mariners have had one of the best pitching rotations in baseball for the last couple of years. Luis Castillo, Bryce Miller, George Kirby, Bryan Woo, and Logan Gilbert make up one of the most talented units in recent memory.

This year, the unit wasn't as good as it has been in the past, but Woo was certainly special. The talented righty was one of the best pitchers in baseball for a bulk of the year, but he's been injured down the stretch. He's yet to appear in a postseason game, though he's expected to return in the near future.

And the Mariners sustained this level of dominance while throwing their fastball more than any other pitching staff in baseball. Seattle's pitchers threw their fastball 55.9 percent of the time this season.

There are a lot of unique fastballs on the team, whether it be because of spin, velocity, approach angle, or another unique metric. But the Mariners have pulled a 180 degree turn in the postseason.

Mariners throwing more off speed with the season on the line

Seattle Mariners pitcher George Kirb — Oct 10, 2025; Seattle, Washington, USA; Seattle Mariners starting pitcher George Kirby (68) reacts after striking out the side against the Detroit Tigers in the fifth inning during game five of the ALDS round for the 2025 MLB playoffs at T-Mobile Park. Mandatory Credit: Steven Bisig-Imagn Images | Steven Bisig-Imagn Images

In the postseason, the Mariners have ramped up their off-speed usage. They lead baseball in postseason slider usage, throwing it nearly 40 percent of the time while the second-place team throws sliders only 20 percent of the time. And this couldn't have been more evident in Friday's thrilling 15 inning victory over the Detroit Tigers.

Kirby, the team's starter, didn't bother establishing his fastball. He threw 50 percent sliders and looked dominant doing so. Matt Brash came out of the bullpen for a few important outs and threw his slider nearly 80 percent of the time, surrendering no real damage on the pitch. Brash mixed in 27 percent changeups and didn't throw a fastball.

Andres Muñoz has a fastball near triple digits, and he threw 22 sliders compared to three fastballs. Gilbert threw 44 pitches and only four were fastballs.

The Mariners are showing new wrinkles to their pitching staff. It's seemingly more than just a one or two game outlier at this point, too. It seems like they're making an adjustment and it's working out in the best way possible.

Only time will tell if the Mariners continue an off-speed heavy approach against the Toronto Blue Jays in the American League Championship Series.

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