Splitting up: Comparing Tanaka's and Iwakuma's Splitter

Masahiro Tanaka and Hisashi Iwakuma have a lot more in common than sharing a dugout and a uniform in Japan a few years ago. Both have excelled as starting pitchers in the United States – Iwakuma's 2.66 ERA since joining the Mariners rotation in July 2012 is the best among AL starters and Tanaka's 2.02 ERA leads the AL this season – and both feature nasty splitters as their primary “out” pitches.

With the two former Rakuten Golden Eagles teammates set to go on back-to-back nights in Seattle, here's an in-depth look how the two pitchers have dominated hitters with that signature split-fingered fastball.

Stats don't lie The results have been nearly identical for both Iwakuma and Tanaka this season when they throw their splitter. Iwakuma has a 23-point advantage in OPS allowed thanks to a few more walks allowed with the pitch by Tanaka, while both are holding batters to nearly identical batting averages and slugging percentages.

Hisashi Iwakuma vs Masahiro Tanaka Splitter This Season
Pitches BA OBP SLG
Iwakuma 165 .133 .133 .183
Tanaka 310 .135 .150 .189

They both throw the pitch about 25 percent of the time in all counts and 40 percent of the time when ahead in the count, while Iwakuma leans on his splitter a little bit more in two-strike counts (50% vs 41%).

Both pitchers also feature the ability to throw their splitters for strikes at a high rate while at the same time getting batters to chase at their offerings outside of the zone frequently. That is a unique skill that makes the pitch so effective for both pitchers.

Hisashi Iwakuma vs Masahiro Tanaka Splitter This Season
Swing pct Strike pct Chase pct
Iwakuma 65% 69% 52%
Tanaka 66% 70% 57%

The other key similarity in their splitters is the location. Both like to bury the pitch at the knees and away from the batter. More than 80 percent of the splitters thrown by Iwakuma and Tanaka are in the bottom third of the zone or lower, and almost 50 percent are thrown to the outer third of the zone or just off the outside corner.

Different Strokes, Different Folks While both splitters are knee-bucklers and nearly unhittable, there are some noticeable differences in the velocity/movement of the pitches and how Tanaka and Iwakuma use it to get outs.

Tanaka throws his splitter harder, averaging 86 mph compared to 84 mph for Iwakuma, while Iwakuma's splitter has nearly twice as much horizontal movement as Tanaka's.

During his short career Tanaka has proven to be one of the best strikeout pitchers in the league, so it's no surprise that his splitter is much more of a swing-and-miss pitch than Iwakuma's. Instead of getting batters to whiff at his splitter, Iwakuma simply makes them pound it into the ground with a groundball rate of nearly 80 percent on the pitch.

Hisashi Iwakuma vs Masahiro Tanaka Splitter This Season
Avg Vel Groundball pct Miss pct
Iwakuma 84.1 mph 78% 27%
Tanaka 86.3 mph 67% 41%

Tanaka's swing-and-miss splitter was in full effect against the Angels on April 27. He threw 30 splitters, with eight of the 12 outs against the pitch coming via strikeout while the Angels missing on more than half of their swings vs the pitch.

Iwakuma's worm-burning splitter was at its best against the Rangers on May 20. He threw 20 splitters, and while only four were put in play, all four of those resulted in groundball outs including one double play.

Regardless of the differences in their split-fingered fastballs, there is one constant: batters have not been able to figure out how to make solid contact and continue to flail hopelessly at the pitch.