Masahiro Tanaka has been a fine pitcher this season. His strikeouts are down, but they’re still above league average. His walk-rate is a tick up, but he’s still in a good spot there. He’s allowing home runs well below his career average, as that’s been helpful. His xwOBA against of .295 correlates fairly with his wOBA against of .303, so either way you look at it there, he’s been good. By the accounts of ERA, FIP, xFIP, and SIERA, he’s been pretty solid this season to date.
In terms of strategies and results, not a whole lot has changed with Tanaka this year. His fastball velocity is stagnant and he’s still using his wide mix of pitches. Outside of throwing his slider a bit more, nothing has really changed in his pitch usage.
Like previous seasons, Tanaka’s four main pitches this season have been his four-seamer, splitter, slider, and sinker. For the sake of intrigue, I’m going to ignore his splitter for a second. Looking at the xwOBA on the remaining three of his four main offerings, he looks to be in fantastic shape. The sinker got destroyed at a .457 clip in 2018. This season it’s down to .356. The four-seamer has seen significant improvement, falling from .408 to .359 this season, his best mark since the 2016 season. The slider’s xwOBA is also down from .247 to .209. If you were to look at this visual solely, you’d think Tanaka is in great shape.
There’s bad side though, which has to do with my leaving his second most used offering, his splitter, out of that visual. Throughout Tanaka’s career, his signature pitch has been his splitter.
To look at the rare dominance he’s put with this offering, I exported data on every pitcher in the pitch tracking-era with at least 100 innings thrown at a five percent or great splitter usage. Going back to 2007, that gives us a sample size of 41 pitchers, ranging from Jae Seo to Freddy Garcia to Roger Clemens. Tanaka’s combination of using splitter and getting results on it has built up a uniqueness in recent years. Among those 41 pitchers, not one has thrown the splitter at a higher rate than him (27.6 percent) and only three have put up a higher prorated pitch value on the splitter. Two of those pitchers (Cory Lidle, Julian Tavarez) threw the pitch less than 15 percent. The only one comparable to Tanaka in usage and results has been Roger Clemens.
The Statcast data would back this up too. In the Statcast-era (before 2015) among pitchers with at least 500 results, only Kevin Gausman and Hector Neris have a lower xwOBA on their splitter than Tanaka.
This season, there are 26 pitchers with at least 25 results on their splitter. Masahiro Tanaka ranks 24th in xwOBA at .338. Only Charlie Morton and Alex Cobb are worse. The results on it this season aren’t even in the same vicinity as his career usual. Tanaka, for at least the moment, has lost his splitter.
Initially, it was hard to figure out what’s been causing this. Tanaka is throwing the splitter with a comparable velocity (it’s up 0.1 MPH). All of his other pitches have been better, so you’d figure that’d only help it. But there does seem to be something clear with the vertical movement on the offering, perhaps the most important component. If you look at his other main three offerings, the percentage of drop looks comparable to his previous seasons.
Meanwhile, his splitter...
Last season, Tanaka’s splitter was below average in vertical movement, ranking 20th out of 35 qualified pitchers. His above average velocity on command of it keep the pitch in check though. This season, it ranks 24th out of 26 qualified. That change in movement has taken a tole on his results.
- 2014: 55.7% O-Swing%, 28.2% SwStr%
- 2015: 56.1% O-Swing%, 19.8 SwStr%
- 2016: 50.2% O-Swing%, 16.9% SwStr%
- 2017: 55.85% O-Swing%, 23.7% SwStr%
- 2018: 55.5% O-Swing%, 21.7% SwStr%
- 2019: 47.5% O-Swing%, 9.8% SwStr%
Hitters are swinging less often outside the zone, taking more often on splitters. This has made it hard for Tanaka to generate swings and misses on the offering, therefore making it hard to get strikeouts, which has subsequently plummeted the pitch’s value.
What seems to be causing the change in movement for Masahiro Tanaka is anyone’s guess. Whether it’s a fluke or something that might stick around is the same. If the struggles with the splitter continue, that leaves a lower margin of error for the rest of his offerings, which would be concerning. For now he’s getting by, even though his signature pitch is missing.