What makes Zach Britton so dominant?

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Zach Britton, the Baltimore Orioles closer, extended his scoreless innings streak to 11 and two-thirds last night as he closed out a 6-5 victory over the Boston Red Sox. He has not allowed a run since a May 16 loss to the Los Angeles Angels in which he gave up three ninth inning runs in a game the Orioles were already losing. Take away those three mop-up duty runs, and Britton has allowed only two other runs all season. That makes for a 0.73 ERA.

On the season, Britton has allowed only one run in a save situation all season. That run came way back on April in a game against the Red Sox. Britton blew that save after allowing two infield singles and then seeing Manny Machado throw a sure double play ball away. Hard to put blame on him for that.

What’s most impressive about Britton’s dominance, is that he is doing it almost solely with one pitch. He has thrown his sinking fastball 89% of the time in 2015. Last season, when Britton had a 1.65 ERA and 37 saves, he threw his sinker 91% of the time. This season, Britton is throwing his slider a bit more frequently, and the result is a massive jump in strikeouts. After striking out 7.3 per nine last season, Britton has struck out 11.6 per nine in 2015.

Some would question the sanity of a manager who is willing to place the closer’s mantle upon a sinker-ball pitcher. When you have a pure sinker-ball pitcher, you do open yourself up to a few more random base hits, as evidenced by that April 25 game in which Britton allowed two infield singles. Britton, however, does not throw a pure sinker in the way that Jim Johnson, whose career went down in flames when his sinker stopped sinking, did. Most pitchers who throw a sinker only get downward movement. Britton is able to generate downward and horizontal movement on his fastball. His movement, which also comes late, combined with his deceptive delivery make his fastball virtually unhittable.

What’s more, unlike most pitchers who rely heavily on a sinker, Britton actually has outstanding velocity. His average fastball this season, according to Pitch f/x data, has been thrown with a velocity of 96 MPH. In last night’s game, he touched 98 several times. In two failed seasons as a starting pitcher for the Orioles, Britton’s sinker topped out around 92.

The combination of late movement, deceptive motion, and velocity have combined to make this fastball nearly as effective as Aroldis Chapman‘s 101 MPH gas. Hitters are batting .238 against Britton’s fastball and .227 against Chapman’s fastball.

One thing that really stands out when trying to boil down what has made Zach Britton nearly unhittable this season is the 43.4% chase rate by opposing batters. Many of Britton’s fastballs finish outside the zone, but the movement comes so late that hitters have already decided to pull the trigger. Furthermore, Britton’s increased reliance on his slider is paying huge dividends. With that slider actually on hitter’s minds, his fastball is that much more effective.

On the season, 13 at-bats have ended with Britton using his slider. Twelve of those were strikeouts, and only one went in the books as a base hit. Hitters have swung and missed at 35.1% of Britton’s sliders and put only 2.7% of them in play. To put that into perspective, Chapman’s slider is put in play 15.1% of the time, and hitters only swing and miss at it 17.4% of the time. Britton is not totally reliant on it as an “out” pitch, but that is exactly what it has evolved into.

Zach Britton flamed out as a starting pitcher and started the 2014 season in limbo for the Baltimore Orioles. An injury to Tommy Hunter opened the door for what seemed a short stint filling in as closer. Britton has not looked back, and cannot be left out of the discussion for most dominant closer in baseball. He is mostly getting by on one pitch, but like Mariano Rivera‘s cutter, Britton’s sinker is that good a pitch.

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