Aroldis Chapman throws a changeup, and I’ve written before about how unfair that is. It’s not the best pitch in baseball or anything, but because Chapman’s fastball might be the actual best pitch in baseball, it seems almost impossible to defend against both the heater and the change, not to mention the slider. When you have to prepare for 100, I don’t know how you adjust on the fly for 88, with the same throwing motion. My favorite fun fact from a couple years back is that, of all the swings against Chapman’s changeup, just one made contact.

Chapman isn’t the game’s only elite reliever, and he’s not the only elite reliever with a signature pitch. When you have an elite reliever with a signature pitch, you can imagine it’s difficult to try to hit anything that isn’t the signature pitch. Take Zach Britton, who within a couple months went from potential waiver bait to shutdown closer. This past year, Britton took another step forward, leaning heavily upon his sinker. It’s becoming a famously dominant sinker, which has been a wonderful development for Britton’s non-sinker.

There’s some chance you don’t realize how amazing Britton most recently was. If that’s the case, he finished 10th in baseball in adjusted ERA, second in baseball in adjusted FIP, and first in baseball in adjusted xFIP. Between years, he nearly doubled his K-BB%, and he just posted the highest groundball rate we have on record. Britton was already good in 2014, but then he improved his sinker command, and he started throwing a little harder. While he threw fewer pitches in the zone, he generated way more swings at pitches out of the zone, so he threw plenty more strikes, and all the rest of the good stuff followed. Britton did everything you want out of a reliever. He even managed to limit hard contact.

The story of Britton’s career is his sinker, which he’s thrown considerably harder since moving to the bullpen. Last year, of all the pitchers with at least 50 innings, Britton threw a greater rate of sinkers than any other pitcher threw of anything. Nine out of every 10 pitches were sinkers, just as was the case the year before, but opponents couldn’t do anything to adjust. Britton’s 2014 ERA was far lower than his FIP, but instead of the former moving up in 2015, the latter went down. Britton’s peripherals adjusted to match his ERA, in a sense. While there are other lefties who throw sinkers with Britton’s movement, there’s not a single one who matches Britton’s blend of movement and velocity.

Elite reliever. Nine out of 10 sinkers. When you face Zach Britton, you know exactly what to prepare for. Odds are, you’re going to get a sinker, and it’s going to be hard, and it’s going to be low. Yet nine out of 10 leaves one out of 10. About 10% of the time, Zach Britton throws a slider. The slider is Zach Britton’s version of Aroldis Chapman’s changeup. It’s less obviously unfair, but it’s unfair nevertheless, and, hell, Chapman’s changeup is his third pitch. The slider is Britton’s second.

Making use of the Baseball Prospectus PITCHf/x leaderboards, I ran some math. I looked at pitches thrown last year that generated at least 25 swings. It’s a low minimum, but we’re not looking into one of the noisiest statistics. Once I had those pitches identified, I sorted in descending order of whiffs per swing. Think of this as just 1 – contact rate. The top five, by this simple measure:

At one point I wrote about Capps. A month later, he was hurt and shut down. What Capps managed to pull off was obscene, and there were several obscene pitches thrown by different pitchers last year, but you see Britton second on that list. When batters swung at his breaking ball, they missed three-quarters of the time. That’s what happens when you swing at a pitch, expecting a sinker, and the pitch isn’t a sinker at all.

This is some pretty standard game-theory stuff. Britton’s slider isn’t really the second-most-unhittable pitch in baseball — if he threw it more, it would get hit more. A big part of its success is its relative infrequency, but it’s still a good pitch, even if the sinker is better. It’s because of the sinker that the slider is so good, and it was good even before Britton improved last season.

Britton showed about the same pitch mix in the last two years, but last year he was much better, and what that suggests is that his sinker got better, and his breaking ball got similarly better. His improvement didn’t come out of one individual pitch; it came out of both, and this post just isolates the slider. Two years ago, the slider was a strike less than half the time. Last year, it was a strike two-thirds of the time. Two years ago, the slider got a strikeout in a two-strike count 30% of the time. Last year, it got a strikeout in a two-strike count more than half the time. In 2014, he gave up one hit on the slider. In 2015, he gave up one hit on the slider. (It didn’t leave the infield.) (An out was still recorded on the play.)

These posts tend to follow something of a template. This part is the part where I’m supposed to embed example video. Who am I to disobey a template?

Even when the batter is looking for something low, which is just about always, the slider drops off the table, and there’s an enormous velocity gap between it and the sinker. The offspeed aspect is the key to the swinging strikes. And though this post is mainly about the whiffs, Britton also picked up his share of called strikeouts on the breaking ball, because no one in his right mind would ever face Britton looking for a slider up:

Britton owns one of the game’s premier sinkers, and opponents know all about it, because he throws it the overwhelming majority of the time. It’s kind of like his own version of the Mariano Rivera or Kenley Jansen cutter, and as an opposing batter you can’t rely on having had much experience against a left-handed sinker thrown so hard. It’s a rare pitch, and Britton has wonderful command of it, and because of how good the sinker is, Britton’s also allowed his slider to become a complementary weapon. He’ll only throw one or two or three per inning, but because of that, and because of the threat of the sinker, it’s remarkably effective, because it’s almost impossible to protect against both. You can think of Zach Britton as a one-pitch closer. Objectively it’s not far from the truth. Yet opponents who think like this discover he’s really a two-pitch closer. This past year they tended to remember that a little too late. Not that the knowledge necessarily would’ve helped.