Zack Wheeler’s slider has been more effective in 2017

Back in 2013 and 2014, Zack Wheeler flashed a wipeout slider, but inconsistencies in command and execution made the pitch below average by some key metrics. Wheeler’s 13.8% swinging strike rate on his slider from 2013-2014 was below the league average of 15.3% on that pitch. Batters hit .230 off his slider with a .350 slugging percentage, both slightly worse than the league averages of .216 and .338 on sliders. Looking at the data alone, the pitch wasn’t particularly exciting.

But Wheeler flashed enough with the slider visually to show you that there was potential for it to be a serious out pitch with improvements in execution. Here’s an example of a well-located 91 mph slider from a start in 2014 with ferocious break:

The pitch is well located because it starts in the strike zone, making it more likely to entice the batter to swing at it, before being buried into the left handed batters box outside of the zone, where the batter will have a difficult time hitting the pitch with any type of authority. The fact that it’s coming to the plate at 91 mph makes it even more ridiculous; the average slider traveled to the plate at 85 mph in 2014, six miles per hour slower than this pitch.

Through his first month in 2017, including two starts against the high-octane Nationals offense, Wheeler’s slider has made strong progress by the metrics. It currently has an excellent 22% swinging strike rate, well above the 2017 league average swinging strike rate of about 16% on a slider, and up from 14% in his last healthy season in the big leagues, 2014. And it is currently second best on the Mets starting staff in swinging strike rate in 2017, behind only Noah Syndergaard.

The outcomes on the pitch have also improved. Batters are hitting .171 against his slider with a .286 slugging so far in 2017, down from a .231 batting average and a .339 slugging in 2014. The pitch has gone from below average to above average by several key metrics.

Part of the reason for the improvement has been location. Wheeler has been more consistent at locating sliders down in the strike zone and below the strike zone in areas that will either generate swings and misses or weak contact. 72% of Wheeler’s sliders have been located in the bottom third of the strike zone or below the strike zone in 2017, an improvement from 55% in 2013 and 2014.

Twice this year, Wheeler has impressively struck out Daniel Murphy with back-foot sliders located down and out of the strike zone. Since the start of last year, Murphy’s 10.1% strikeout rate is fifth-lowest among all qualified hitters in baseball. He’s a difficult batter to strike out, and Wheeler has done it twice in five plate appearances.

Wheeler’s slider has also generated a lot of weak contact. Batters have had a difficult time getting lift on the pitch where they can do damage on it. The average slider generates an average launch angle off the hitter’s bat of about 11 degrees. Wheeler’s has generated an average launch angle of -6.6 degrees, which ranks as the best in baseball on a slider. What this means is that his execution of the pitch has often caused hitters to strike the top of the baseball, which knocks the ball into the ground in front of home, slowing its velocity down and making it easier for Mets infielders to field them.

This slider located down in the zone generates a weak launch angle of -21 degrees and is easily converted into a double play by third baseman Jose Reyes.

And this one located low and away is rolled over with a launch angle of -47 degrees.

Overall, Wheeler has still demonstrated some of the flaws that hindered his potential as a frontline starter prior to his injuries. He’s pitched six innings or more only once in five starts, and it likely would have been six without last Thursday’s game in Atlanta being wiped out due to rain. He’s still falling behind batters more often than average, with a 57% first pitch strike rate, below the league average of about 60%. His 17.5 pitches per inning is also less efficient than the league average of 16.5 pitches per inning.

But looking at some of the positives, he’s made progress with his slider. He’s hit his spots with it more often, and the results in terms of both swings and misses and outcomes have been strong so far. That’s some good to take away from Wheeler’s first month back in the big leagues after he’d missed the past two seasons.