Mariners starters have some of MLB’s nastiest new pitches

When it comes to pitching, few have been better than the American League West leading Seattle Mariners this season.

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With ace-level talents Luis Castillo, Logan Gilbert and George Kirby heading the rotation, plus promising second-year big leaguers Bryce Miller and Bryan Woo, the Mariners sport arguably the toughest starting five in the league. The rotation displayed its talents with a historic run earlier this season, allowing two or fewer earned runs in 21 consecutive games. That was one game short of a 107-year-old MLB record, and it came while the rotation wasn’t at full strength.

One of the special parts of Seattle’s starting five is that 80% of it is made up by homegrown talent, and the development of those players is what has allowed the Mariners to be a playoff contender without an imposing offense in recent seasons. Part of that development is the implementation of new pitches, and this year two Mariners starters have added some of MLB’s nastiest.

ESPN MLB insider Jeff Passan on Friday wrote about the 12 best new pitches for hurlers in 2024, and Gilbert’s cutter and Miller’s splitter were among those featured.

Logan Gilbert’s cutter

The 27-year-old Gilbert is a self-described pitching nerd and always looking for new ways to improve his repertoire. He added a split-finger fastball to replace his changeup last season, a decision that paid off handsomely as opponents batted just .174 off the pitch. Gilbert added a cutter to his arsenal this season, and the early returns have been fruitful. Opponents were hitting .244 off the cutter entering Saturday, and it’s been Gilbert’s third-most-used pitch at 16.9%.

That .244 average is actually the highest among the five pitches Gilbert has thrown most this season, but it’s the underlying numbers that show just how devastating his cutter is. Passan pointed out that Gilbert’s version of pitch grades out as MLB’s best cutter according to the FanGraphs metric Stuff+, which uses a number of factors combined to measure how nasty a pitch is. According to Statcast, Gilbert’s cutter has 20.5 inches of vertical drop and four inches of horizontal break, which are 4% and 22% above the MLB average, respectively. The 92 mph he averages on the pitch is tied for 14th best among all pitchers and ninth among starters.

The effect the cutter is having on the rest of Gilbert’s pitches is where the addition of the cutter stands out most in terms of results. Gilbert’s four-seamer, slider, splitter and curveball have all seen drops in opponents’ batting average through the right-handers first 10 starts, and the slider is the only of those four that hasn’t seen a drop in opponents’ slug.

“We’ve kind of seen (him) learning how the cutter is fitting into the whole mix and when to use it, where to use it and how to help it set up his primary weapons like his slider and his split,” Mariners pitching coach Pete Woodworth told Seattle Sports’ Bump and Stacy earlier this season.

Bryce Miller’s splitter

In a recent interview, Miller admitted he has a tendency to steal from Gilbert due to the pair’s similarity in pitching styles. So naturally Miller added a splitter in lieu of a changeup a season after Gilbert, and the 25-year-old Texan is seeing the same sort of positive results. Miller struggled immensely with left-handed batters last season, surrendering a .303/.358/.558 slash line compared to .200/.234/.315 against righties. With the splitter now in the fold specifically to combat those problems, lefties are hitting .170/.240/.407 off Miller this season.

The splitter has quickly become Miller’s most effective pitch. Opponents’ .154 batting average and .212 slugging are the lowest against any of his five pitches. Miller’s version of the pitch features a particularly sharp downward break with an average of 4.8 inches, 13% above league, while it’s horizontal movement of 7.7 inches in well below league average.

Passan pointed out that the location of the pitch is what’s helped it become so useful. Miller’s splitter leads the league in Fangaphs’ Location+, which grades a pitcher’s ability to locate pitches well, adjusted to count and pitch type.

The pitch has also helped Miller’s strong fastball become more effective. Batters are hitting .167 with a .333 slugging through Miller’s first 10 starts as opposed to a .256 average and .450 slug last season.

“It’s helped him a lot,” Mariners manager Scott Servais said earlier this month. “It’s more of an action pitch. The changeup, some guys just don’t have a great feel for the changeup. Logan had a hard time with it. Miller (had) a hard time with it, but the guys who especially throw hard like that, just grip it a little different (and) throw it like a fastball. It’s got good action to it (and) he’s been throwing it around the plate close enough so hitters will offer at it.”

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