Hisashi Iwakuma - Baseball's Best Splitter

Otto Greule Jr

Hisashi Iwakuma has been dominant this season, and much of it is thanks to his hard stuff. Here's a deeper look at his usage of the splitter, and how effective it's actually been.

Despite Sunday's minor speed bump, Hisashi Iwakuma has been one of baseball's best starting pitchers over the past calendar year. Iwakuma commands an arsenal of five different pitches that he peppers the plate with, and his splitter has proven to be spectacular.

Iwakuma throws five pitches. They are a four-seam fastball, sinker, slider, curveball, and split. He mixes his pitches up with great frequency, not throwing any one of them more than 30% of the time.

Trajectory and Movement - 2013 season

Pitch Type Count Freq Velo (mph) pfx HMov (in.) pfx VMov (in.) H. Rel (ft.) V. Rel (ft.)
Fourseam 441 29.44% 90.57 -6.89 8.02 -2.63 5.34
Sinker 369 24.63% 89.92 -9.8 3.64 -2.65 5.34
Slider 271 18.09% 81.49 3.79 0.59 -2.6 5.35
Curve 95 6.34% 72.41 7.57 -4.55 -2.34 5.57
Cutter 1 0.07% 82.57 -2.88 6.35 -2.74 5.42
Split 321 21.43% 86.38 -8.07 -0.79 -2.6 5.43

Iwakuma's usage of those pitches is as follows.

Pitch Usage - from 01/01/2013 to 01/01/2014

Fourseam Sinker Cutter Slider Curve Split

All Counts 26% 27% 0% 10% 8% 29%
First Pitch 41% 27% 0% 8% 14% 10%
Batter Ahead 25% 50% 0% 8% 3% 14%
Even 31% 26% 0% 10% 12% 21%
Pitcher Ahead 20% 17% 0% 12% 5% 45%
Two Strikes 22% 18% 0% 5% 3% 53%

All Counts 33% 21% 0% 27% 5% 13%
First Pitch 45% 19% 1% 27% 6% 2%
Batter Ahead 36% 35% 0% 20% 1% 7%
Even 37% 19% 0% 27% 6% 11%
Pitcher Ahead 26% 15% 0% 31% 6% 22%
Two Strikes 30% 12% 0% 23% 2% 33%

As is the case with many pitchers, Iwakuma leans on his fastball to get ahead in the count against either kind of batter, but the usage of his other opening counts is interesting. Iwakuma uses sliders on first pitch 27% of the time against RHH, and in general rarely uses it against LHH. Conversely, Iwakuma elects to attack LHH with his split, especially when he's ahead in the count or has him on two strikes, where he throws it more than half the time (53%). The split has become a dominant pitch for Iwakuma, as even against RHH, it is his primary pitch late in at-bats, despite it's lower usage throughout the rest of the at-bat. While Iwakuma still uses the slider frequently against RHH, it is his secondary out pitch.

Let's take a further look into Iwakuma's split, and the results that it generates. First, the overall usage.

Pitch Outcomes - 2013 season
Pitch Type Count Ball Strike Swing Foul Whiffs BIP GB LD FB PU HR
Fourseam 441 31.29% 35.83% 42.40% 18.82% 10.66% 13.83% 4.31% 3.40% 4.76% 1.36% 0.91%
Sinker 369 26.83% 23.04% 55.01% 21.95% 5.15% 27.91% 15.18% 5.42% 6.78% 0.54% 0.81%
Slider 271 28.78% 38.38% 46.13% 14.02% 13.65% 18.45% 5.17% 4.06% 6.27% 2.95% 1.11%
Curve 95 46.32% 36.84% 23.16% 5.26% 7.37% 10.53% 5.26% 0.00% 4.21% 1.05% 0.00%
Cutter 1 0.00% 100.00% 100.00% 0.00% 100.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%
Split 321 33.02% 23.68% 62.93% 21.81% 20.56% 21.50% 16.51% 3.12% 1.56% 0.31% 0.00%

Iwakuma's split generates a 62.93% swing rate, and part of that can be attributed to how heavily it's used with two strikes. Iwakuma's yet to allow a home run on it this year.

There's a reason Iwakuma uses his split more against lefties than righties. Take a look at this table that breaks down what's happening between both hitters.

LHH 32.14% 83.33% 15.58% 2.08%
RHH 25.81% 61.90% 14.29% 19.05%

Left-handed hitters have not been able to get this pitch into the air, and swing and miss more often. As you can see, Iwakuma also generates a ridiculous 83% of balls in play on the ground to left-handers. While the pitch doesn't appear as effective against right handers, he doesn't use it nearly as much (13% compared to 29% vs. LHH) for a reason.

Yet, the end results against RHH this season have been wildly dominant.

LHH 0.195 0.221 0.026 0.319
RHH 0.088 0.088 0 0.143

Here's where Iwakuma throws the split versus lefties - down and away, down and away.


via pitchfx.texasleaguers.com

Versus righties, it's simply...down. As splitters do.


via pitchfx.texasleaguers.com

When Iwakuma gets two strikes on a hitter, the end results for the split are absurd.

LHH 0.098 0.098 0 0.194
RHH 0.103 0.103 0 0.188

Iwakuma also generates a combined 32.82% whiff/swing rate with 2 strikes, which isn't far off from his split whiff rates in total.

This is a dominant pitch. Iwakuma has a wSF of 8.5, making it the most valuable split in the game so far. On a per pitch basis, Ryan Dempster has been slightly better (3.18 wSF/C) over Iwakuma's (2.98), but Dempster throws the pitch 16.6% (a career high) of the time compared to Iwakuma's 21.4%. Iwakuma throws his split more than anybody else in the game, just ahead of Hiroki Kuroda (19.3%).

While Iwakuma's split has been dominant, his four-seam & sinker are nearly as fantastic. Brooks Baseball provided the charts above, and separates out each pitch. For wFB, Fangraphs combines different fastball usages, including Iwakuma's four seam and sinker. Together, they grade out to a wFB of 13.4. Here are the four pitchers who have higher wFB than Hisashi Iwakuma this season.

Name wFB
Cliff Lee 18.5
Matt Harvey 16.5
Clayton Kershaw 16
Mike Minor 14.4
Hisashi Iwakuma 13.4

Hisashi Iwakuma has the most effective fastball (combined usage) in the American League. When you sort it by wFB/C, Iwakuma ranks 3rd in all of baseball, as his overall usage is lower than Minor and Kershaw.

Simple conclusion - Hisashi Iwakuma has been better than anybody else in the AL when he throws the ball over 85 mph.

You can look at the results alone to grade how spectacularly great Hisashi Iwakuma has been, but it is worth looking deeper into why he's so dominant, to further understand why he throws pitches to certain batters and in what situations. I really recommend pouring through the numbers at Brooks Baseball and Texas Leaguers yourself, as you can sort and evaluate the data any number of ways.

All tables are courtesy of Brooks Baseball.

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