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James Paxton throws hitters a (knuckle) curveball

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After breaking out in 2016, the Mariners southpaw has started leaning on his breaking ball more heavily, and it’s working great.

Houston Astros v Seattle Mariners
Paxton’s got curves for days.
Photo by Stephen Brashear/Getty Images

A week-plus into the 2017 season, just about everything possible has gone wrong for the Mariners. Jean Segura hit the DL with a hamstring strain, Robinson Cano has looked more like his 2015 self, and Kyle Seager has fallen far short of expectations. Nelson Cruz, in a fit of anger, appears to have stabbed repeatedly at the portrait hidden away in his attic. Felix Hernandez isn’t what he used to be, and Hisashi Iwakuma has gotten Weaveritis. Yovani Gallardo and Ariel Miranda have shown why the Orioles wanted to get rid of them. And even rising star Edwin Diaz imploded during the team’s disaster on Sunday.

Really, only one established player has surpassed expectations, and by quite a bit. After several years of injuries and ineffectiveness, former Mariners top prospect* James Paxton put up a solid 3.79 ERA in 121 innings last year. And over two starts this season — both against the Astros, who have one of the best offenses in the majors — Paxton has pitched 13 innings and allowed zero runs. Even with Seattle collapsing around him, the budding southpaw has continued to develop into one of MLB’s best starters.

*Second only to “just a bit outside” as the most cringe-inducing set of four words in the baseball lexicon.

Paxton’s story is a little more complicated than that, though. While he had an unspectacular ERA in 2016, his 2.80 FIP really stood out. In that regard, he was a better pitcher than Max Scherzer and Rick Porcello, the NL and AL Cy Young winners, respectively. Paxton had issues because he underperformed his peripherals, posting the second-highest BABIP in baseball at .347.

In 2017, though, he’s gotten the best of both worlds. Thanks to an uptick in strikeouts (and zero home runs allowed, which is pretty lucky), Paxton has improved his FIP to 1.68. At the same time, he’s whittled down his BABIP to .182. And while it’s obviously rather early in the season, Paxton’s made some changes to the way he pitches as well, which provide an explanation other than “randomness” for his step forward. Take a look at his pitch usage over the last two years:

Image via Brooks Baseball

He’s thrown the curveball — technically a knuckle-curve, but Brooks doesn’t use that distinction — nearly twice as often this year (25.3 percent) as he did last year (13.7 percent). That pitch has taken the place of the changeup, sinker, and cutter; it’s the latter offering that’s most curious.

Last season, Paxton’s cut fastball was one of the most deceptive in the majors. With an average velocity of 90.3 mph — 11th among starters with at least 100 thrown — his cutter consistently blew past hitters:

Highest cutter whiff rate — 2016

Rank Player Cutters Cutter Whiff%
Rank Player Cutters Cutter Whiff%
1 Max Scherzer 133 26.3%
2 James Paxton 309 23.6%
3 Bud Norris 213 20.7%
4 Yu Darvish 148 15.5%
5 Corey Kluber 766 15.3%
6 Chris Tillman 440 15.0%
7 Jon Lester 737 14.2%
8 Drew Pomeranz 331 14.2%
9 Rick Porcello 263 14.1%
10 Nathan Eovaldi 148 13.5%
Rankings among 69 starters with 100+ cutters thrown in 2016. Data via Baseball Prospectus

(For a more in-depth breakdown of what made the cutter so great, check out Ethan Novak’s superb analysis over at Lookout Landing.)

The curveball was pretty nasty, too — it had an 18.1 percent whiff rate, which ranked eighth among 100 starters — but it couldn’t compare to his cutter. So why has Paxton emphasized the knuckle-curve this year?

Hitters put Paxton’s curveball in play 37 times last year, with an average exit velocity of 85.4 mph; that ranked 32nd out of 138 pitchers with at least 25 balls in play off the curve**. His cutter, on the other hand, placed 68th out of 73, zooming off the bat at 91.0 mph. Paxton’s 91.0 mph overall exit velocity was one of the highest in baseball, which had a hand in his elevated BABIP.

**This includes curveballs and knuckle-curves.

So this season, by focusing more heavily on the knuckle-curve, he’s given up some of the cutter’s whiffs in exchange for much more weak contact. His curveball (78.5 mph average exit velocity) has remained better than his cutter (82.8 mph) in this regard, and his exit velocity as a whole has plummeted to 83.2 mph, one of the lowest in baseball. Plus, it hasn’t really been much of a sacrifice: the curve still gets lots of swings-and-misses, so Paxton hasn’t lost any strikeouts. As stated earlier, it’s very much the best of both worlds, and it’s why he’s looked so dominant to this point.

If you follow the Mariners on Twitter — and you should — you might have seen this tweet last week:

It’s a tantalizing pitch, to be sure, but it doesn’t fully encapsulate what makes Paxton’s knuckle-curve so masterful. Instead, I prefer this GIF, from his start on Monday:

GIF via MLB.tv. Also, h/t to Chris Anders for GIFing it.

While Jose Altuve managed to put that pitch in play, he didn’t square it up — and he’s not the only hitter to have (for lack of a less clichéd way of phrasing it) trouble with the curve. Paxton’s knuckle-curve gets both whiffs and soft contact, making it one of the better out pitches in the majors. Now that he’s decided to throw it more often, Mariners fans might just have something to look forward to.


Ryan Romano is the co-managing editor for Beyond the Box Score. He also writes about the Orioles for Camden Depot, sometimes. Follow him on Twitter if you enjoy angry tweets about Maryland sports.