Fastballs still get all the glitz and glamour in the major leagues; who doesn’t like seeing the radar gun flash 100 mph? But one breaking ball that has quietly been picking up steam in recent years, figures to play a starring role in this pitching-heavy World Series matchup between the Houston Astros and Washington Nationals: the slider.

Two of Houston’s aces, Justin Verlander and Gerrit Cole, used sliders to great success this season. So did Max Scherzer and Patrick Corbin, two of Washington’s top-of-the-rotation starters. Washington reliever Tanner Rainey also has used his sneaky slider, which has a ton of movement, to help the Nationals stabilize their bullpen in the postseason. And no major league teams have had more success with that pitch than the Astros and Nationals, whose sliders rank first and second in lowest batting average against.

Washington threw 244 sliders (16 percent of pitches) in the playoffs to get to the World Series, limiting opponents to eight hits over the 63 at-bats that ended on that pitch (.127). Just two of those hits, doubles by the Los Angeles Dodgers, went for extra bases. The Nationals threw 3,950 sliders during the regular season and playoffs combined (15.4 percent of pitches), holding opponents to a .185 average on at-bats that ended with sliders, second only to Houston. The Astros threw more than 5,000 sliders in 2019, playoffs included, accounting for almost 20 percent of their pitches. Hitters managed a league-low .176 average against Houston’s sliders.

So what, exactly, is this pitch? The slider is a cross between a fastball and a curve, with the pitcher using a similar grip and arm speed as he would for a two-seam fastball. But the grip for a slider involves greater middle-finger pressure, causing the pitch to have horizontal movement rather than just vertical break.

“What makes a good slider is the break and how much you can make it look like a fastball,” explained Al Leiter, a baseball operations adviser for the New York Mets and analyst for MLB Network during the World Series.

“It doesn’t pop out of your hand and go up; it comes out of your hand like a fastball,” Leiter said in an interview. “There’s no popping up. If a pitcher doesn’t have really good acceleration through his arm speed, the ball pops out of his hand, letting the hitter see it a little sooner.”

“And if you’re going to be a starter,” Leiter added, “you need two pitches at varying speeds that break.”

One of those breaking pitches will be a curveball and the other will probably be a slider. This season, in fact, has seen the most sliders thrown, as a percentage of overall pitches, of any season since 2002, the first year data is available. That increase came almost exclusively at the expense of fastballs. And 2019 was the fifth straight year that baseball’s percentage of sliders increased.

Scherzer, Washington’s Game 1 starter, delivers one of the filthiest sliders in baseball. The Nationals’ ace has amazing control with the pitch and will regularly use it against right-handed batters, whether he is ahead or behind in the count. Scherzer elicited swinging strikes on more than 50 percent of his sliders, by far the highest percentage of any of his pitches. And thanks to a nearly 10-mph difference in average velocity between his four-seam fastball (95 mph) and slider (86 mph), he also caused batters to swing and miss at that breaking ball 28 percent of the time.

Overall, batters are hitting just .159 against Scherzer’s slider this season, with 69 strikeouts in 164 at-bats ending on the pitch. Scherzer’s slider saved the Nationals almost four runs per 100 pitches thrown in 2019, the second-most runs saved on sliders of any qualified starter who threw at least 500 sliders.

Corbin, a left-hander, also has an effective slider, in his case one that dives away from left-handed hitters and toward the feet of right-handed hitters. But unlike Scherzer, who uses his slider to complement his primary pitch, which is a fastball, Corbin’s slider is his bread-and-butter pitch. Its sweeping break moves four inches toward a right-handed batter and drops 42 inches. A league average slider at a similar velocity has 39 inches of drop. The net result: Opposing hitters are batting .164 against Corbin’s slider, with 166 strikeouts in the 312 at-bats ending with that pitch.

Relievers don’t get to throw the slider as often, but when they do, it can be a powerful weapon. Rainey’s slider drops 39 inches, five inches more than similar major league sliders at his velocity (87 mph), and he held opposing batters to a .127 average with 46 strikeouts in 79 at-bats ending on the pitch. Rainey and his slider could be pivotal for Washington out of the bullpen. He has allowed just one home run in 72 plate appearances that ended with the pitch, and he has gotten batters to hit a groundball off the pitch six out of every 10 times a ball is put in play. Just 10 of the 261 sliders he threw were hit on the sweet spot of the bat.

The key? Yet again, it’s deception. The release point for Rainey’s slider is almost identical to that of his fastball.

The Astros counter with powerful sliders of their own, and they rely on the pitch even more than the Nationals do; they threw the pitch almost 20 percent of the time, second most of any playoff team. Verlander’s slider produced a 41 percent overall strikeout rate and saved Houston more than three runs per 100 times thrown, making it the third-best slider in the majors this season, one spot behind Scherzer’s. He throws it hard (88 mph, topping out at 91) with above-average spin (2,612 revolutions per minute) and, as with his fastball, he isn’t afraid to attack hitters in the strike zone with the pitch. Hitters, on the other hand, haven’t figured out what to do with it. They are batting .255 against Verlander when his slider is thrown in the heart of the strike zone, compared with .310 against every other pitcher who enters the same zone with a slider.

The slider was also one of the tools Cole used to become the AL Cy Young Award front-runner. His slider saved almost two runs per 100 times thrown (ninth best in baseball), and he held opponents to a .183 average with 100 strikeouts over 246 at-bats ending on the pitch. Cole’s slider is thrown extremely hard (89 mph, one of the fastest sliders among starters) and generated a swinging strike better than once every five times thrown in 2019, a career high for Cole. Hitters are also making less contact on the pitch outside the strike zone this season, perhaps because they’re chasing it more often.

While both Houston and Washington are effective when throwing sliders, their success at hitting the pitch is quite different. The Astros are slugging .488 against sliders during the regular season and playoffs, 47 points higher than the next-best team, while the Nationals rank 20th, slightly below the major league average.

Key Washington hitters who have struggled with the slider this year include Juan Soto (20 for 110, .182 batting average), Trea Turner (24 for 120, .200), Victor Robles (30 for 144, .208) and Adam Eaton (25 for 116, .216).

Houston has seen just one of its big bats, Carlos Correa, struggle against the pitch (12 for 69, .174). Alex Bregman, Yuli Gurriel, José Altuve and George Springer are a combined 127 for 445 (.285) against sliders in 2019, including the playoffs. Altuve even clinched his team’s World Series berth on a Aroldis Chapman slider, launching it over the left field fence Saturday night. He should get plenty more chances against sliders this week.

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