The Astros Need to Solve Masahiro Tanaka’s Slider

If Masahiro Tanaka has a signature pitch, it’s his slider. When he first came over from Japan in 2014, nearly half of his strikeouts came on the splitter despite throwing it only a quarter of the time. In his first three seasons in the majors, Tanaka threw his splitter more often than any other pitch and batters put up a feeble 37 wRC+ against it, while whiffing on the pitch 19% of the time. But in 2017, Tanaka used his slider more often than the splitter. In 2018, that trend continued; he got better results from his slider than he did with the splitter. This season the disparity in usage and effectiveness grew. Tanaka struggled with his splitter due to changes in the baseball, but even after re-configuring the splitter in July, his slider has remained his best pitch.

Against the Astros in Game 1 of the ALCS, Tanaka got eight swings and misses. Every single whiff came on the slider. Here’s how Tanaka’s usage of his slider has compared to that of his splitter this season:

We can see later on in the season where Tanaka felt more confident in his splitter, but as the season ended, the slider was still his primary offering. On the year, Tanaka threw his slider 36% of the time and he’s maintained that heavy usage in the playoffs, with it accounting for 45% of his pitches against the Twins, and 40% of those in the first game against the Astros. Here’s what happened on those 27 sliders against the Astros earlier this week:

Tanaka got eight of the easiest outs possible on those 27 sliders. The xwOBA on the three balls in play was .015. José Altuve saw more sliders than any batter in the first game. In his first plate appearance, he swung and missed on a slider out of the zone, and then popped out on another slider out of the zone. Altuve saw five sliders in this next plate appearance. Let’s go pitch by pitch:

While Tanaka went with a couple sliders out of the zone to Altuve in the first inning, he threw one to Altuve that would have been a strike even if he hadn’t swung. He threw a first-pitch slider to nine Astros batters in Game 1, with four in the zone and five out of it. Of the pitches in the zone, two were called strikes and two were swinging strikes. Of the pitches out of the zone, Gary Sánchez framed one just below the zone for a called strike and two were swinging strikes, while Carlos Correa took two sliders for balls. Part of the reason the slider has taken over for Tanaka is his ability to get strikes both in and out of the strike zone. He throws his slider in the strike zone 47% of the time, more than four percentage points higher than average. Deciding whether or not to swing is a tough choice, and hitters often get it wrong.

Getting back to the Altuve plate appearance, Tanaka had, at this point, thrown three sliders to Altuve and he’d swung at all three, so Tanaka went way out of the zone:

Tanaka then threw Altuve his first splitter, but it was a little low and outside. He might have induced a swing if the pitch had been closer to the middle of the plate, but with the arm-side movement of the splitter, that pitch looked like a ball from the start so Tanaka either needed to get it up a little to steal a strike or put it more over the plate to go for the swing and miss:

With the count shifting in Altuve’s favor, Tanaka refused to give in and threw another slider out of the zone:

Altuve didn’t chase and was now in a good position to look for a pitch to hit. But part of the problem with looking for a good pitch to hit against Tanaka is the wide range of attack. Tanaka might throw his fastball, but when behind in the count this year, a fastball only came about a third of the time, and only around 20% of the time did he serve up a fastball in the zone. As percentages dictated, Altuve did not see that fastball:

Tanaka threw a splitter moving toward the middle of the plate, but the result was a swing way out ahead of the pitch and a harmless foul ball. When batters do make contact with the downward moving pitch, it is a groundball more than 60% of the time. Hitters do a good job of swinging and making contact on splitters in the zone, but the movement of the pitch generally produces groundballs like Altuve’s foul. With the count now 3-2, Tanaka threw another pitch in the strike zone:

Again, a pulled foul ball. Tanaka had thrown Altuve six pitches in this at-bat, and eight on the day, and not a single fastball. If Altuve was looking for a fastball, and got the splitter, he ended up pulling the pitch foul on the ground. If he was looking for the splitter and got a slider, the ball moved to the end of his bat like it did above. After those breaking pitches in the zone, Tanaka looked to end the at-bat:

That slider was just out of the zone, but if he had thrown a splitter or fastball in the same way, those pitches would have been right over the plate, as there’s 9-10 inches of horizontal movement difference between the slider and the other two primary options for Tanaka. Forty-seven of his 68 pitches were either sliders or splitters in Game 1. There were 20 fastballs for Astros hitters to key in on, but only 10 were in the strike zone. Such a low percentage of hittable fastballs makes looking for the pitch a poor strategy, and if a batter isn’t prepared, the hittable pitch gets taken for a strike. Of those 10 fastballs in the zone, five were taken for strikes. When Tanaka can make batters uncertain, he wins the at-bat, and more often than not, hitters are uncertain:

Batters swing at a lot of pitches outside the zone against Tanaka, which is primarily due to a high chase rate on splitters out of the zone. If a batter is looking for the splitter and identifies it as a ball, the different movement on the slider and fastball mean a called strike for Tanaka. Batters swung on 51% of split-fingered fastballs out of the zone during the season, but the Astros did a good job with the splitter against Tanaka. Of the 18 splitters, Astros hitters took seven of the nine offerings outside the strike zone, swung at eight of the 13 pitches in the zone, and didn’t swing and miss one time. The rare fastball in the zone and slider in and out of the zone gave Houston hitters trouble all game as Tanaka coasted for six easy innings. Tanaka’s splitter might be his signature pitch, but it was more of a setup pitch against the Astros. Tanaka’s slider won the day. If Astros batters don’t figure out the slider tonight, the Yankees could tie up the series.