Masahiro Tanaka possesses a deep array of pitches. From the moment he came to MLB, there has been constant discussion about his vast arsenal. He has an impressive splitter, a slider, curve, and cutter, as well as a two-seam fastball and a four-seam fastball.
The 2016 season is still quite young, but thus far, Tanaka has all but eliminated the four-seam fastball from his repertoire. He's only started twice this year, but against the Astros on Opening Day, Tanaka threw just a single four-seamer. Against the Blue Jays this week, Tanaka upped his four-seam usage all the way to four pitches.
Why would he curtail his four-seam fastball so severely? Hitters have raked against the pitch. Here's a look at opposing batters' results against Tanaka's heater, compared to batters' results against his secondary offerings, from 2014-2015, courtesy of Brooks Baseball:
Hitters have smashed Tanaka's four-seamer to the tune of a .333 batting average, along with 17 homers over the past two years. He has yielded an an above-average line drive rate of 29.8% against four-seamers put in play, and generated ground balls at a below-average 34.4% of batted four-seamers in his career.
Given the success batters have had against the pitch, it's not exactly stunning to see increased reticence from Tanaka when it comes to throwing it. Exactly how stark has the drop-off been? During his first two years in the majors, Tanaka threw 884 four-seam fastballs, accounting for over 20% of his total pitches. In his two starts in 2016, his five four-seamers represent just 2.79% of his repertoire.
Of course, it is very early in the season. Pitch usage, like every other metric, is still quite influenced by the vagaries of small sample sizes. Tanaka's apparent reluctance to utilize his four-seamer could potentially be explained away by the tiny sample that is available.
Still, a decrease in usage as dramatic as Tanaka's feels too steep to be waved away on account of a small sample. Could there be alternate reasons, other than admittance of its ineffectiveness, for this decrease? Perhaps Tanaka always starts the season throwing fewer four-seamers, when the cold early season weather dampens velocity.
This hypothesis doesn't appear to hold up, though. Tanaka used his four-seamer over 24% of the time during his first month in the majors back in 2014, and used it 20% of the time during April of 2015. Maybe Tanaka was hesitant to use his four-seamer against Toronto and Houston, two of the best lineups in the AL? If that was his strategy, it was a new one: in six starts against these two teams in 2015, he threw an average of 14 four-seamers. There may be other reasons contributing to Tanaka's aversion to the four-seamer, but at this point, the explanation that he has decreased its usage in response to hitters' success against the pitch seems very plausible.
As he has decreased the use of his four-seamer, he has upped the usage of his splitter, two-seamer, and curve. Here's his pitch usage thus far in 2016, compared to last season:
The results of this experiment, if it can be called that, have been mixed. Tanaka looked solid on Opening Day, but was fairly uneven when he allowed four walks in just five innings against Toronto. His ERA through 10.2 innings stands at 3.84, and he's struck out a strong 22.7% of batters thus far. However, his 11.4 BB% in the early goings is much higher than his career norms.
Would it behoove Tanaka to continue curtailing his four-seam usage, instead of opting for other pitches? His splitter is an excellent pitch, as hitters have batted just .176 against it over the past two years. He has generated whiffs on over 39% of swings against the splitter, and 69.7% of his splitters that are put in play are ground balls. On Tuesday, Tanaka recorded a crucial out with his splitter, fanning Troy Tulowitzki on a 3-2 count:
His slider is also quite useful. Batters hit .150 against it from 2014-2015, and it generated a miss on 36.84% of swings. Here's Tanaka ending the second inning versus Toronto with a nasty slider to Ryan Goins:
Tanaka clearly has the secondary stuff to ease off his fastball, however, some of his success likely would be mitigated if he stopped throwing the four-seamer altogether. Pitches like his splitter and slider generate positive outcomes for Tanaka, but hitters would have an easier time keying onto those offerings if the threat of a 93 mph four-seamer was no longer there.
Tanaka also struggled with his pitch count against the Blue Jays, totaling 54 pitches through just two innings. If decreased use of his four-seamer leads to Tanaka falling behind opposing hitters and driving up his pitch count, it would further pressure an already taxed bullpen. Given that the Yankees' rotation lacks solid candidates to go deep into games, it may be important for Tanaka to pitch deeper in his starts, though it remains to be seen if decreased use of the four-seamer is what's causing Tanaka's inflated early pitch counts.
Overall, it seems that Tanaka should at least keep hitters honest by keeping his four-seamer around. His secondary stuff is great, but it might be less great without a setup pitch. It may be difficult, given opposing hitters success against the pitch, but Tanaka would do well to rediscover confidence in his four-seamer.