As Zack Wheeler continues his development into a premier pitcher, much of his success can be attributed to his changeup.
Zack Wheeler's road to Major League Baseball was predicated on his fastball. His ability to light up radar guns, seemingly with ease, was a major factor in his high prospect rankings and the Mets' desire of him in the Carlos Beltran trade. That said, what gets you to the majors is often not what keeps you there, and according to MLB.com's Tim Healey, it has been Wheeler's changeup that has turned him from above average rookie into stud stopper.
Last week, our own Sean Cunningham argued that Wheeler's changeup was dragging him down, suggesting:
The lack of development with his changeup is supported by Fangraphs’ PITCHf/x pitch values, where a score of zero is considered average, a negative score below average, and a positive score above average. Last season, the ineffectiveness of Wheeler’s curveball—which was assigned a pitch value of -3.6—was a major concern. But this season it has improved significantly and increased to 1.2.
Wheeler’s changeup has made no strides, as it was valued at -0.2 last season and -1.9 this season. Pitch values are far from perfect, but in this case they support what is clearly evident from watching Wheeler pitch.
However, Healey looks at the data a bit differently:
Opposing batters are hitting .255 against Wheeler in at-bats ending with changeups, a considerable drop from the .333 mark they posted in 2013, according to brooksbaseball.net, a website that tabulates such data.
Wheeler's changeup induces one-quarter fewer line drives this year compared to last, and twice as many ground balls. Nearly half of all balls in play on Wheeler's changeups are hit on the ground.
That's what Wheeler wants -- weak contact.
Healey goes on further to suggest that there is a mental aspect to Wheeler's changeup as well. The addition of another seemingly improving pitch gives the batter something more to think about, and even if he lacks feel for it on a given night. It can still be used to slow down a bat, given its stark contrast to Wheeler's high-90s fastball.
Looking at Fangraph's PITCHf/x tool gives us some insight into just how Wheeler's changeup has changed. Wheeler does not throw the changeup often, only having thrown it 42 times last season and 98 times so far this season, but his ground ball percentage has gone from 20.0 percent to 46.7 percent—a marked improvement. Furthermore, Wheeler is getting batters to swing at it more often, as his swing percentage at the pitch outside the zone has improved from 26.7 percent to 29.1 percent, and batters are swinging at changeups in the zone 91.7 percent of the time compared to 75.0 percent of the time last year.
Other stats, however, indicate that despite the changes, the value of Wheeler's changeup has decreased from a nearly league-average pitch, into a below-average pitch, as its Fangraphs pitch value has decreased from -0.23 to -1.56. That number has improved even over his past three starts, as it sat at -1.9 last Monday.
Since the All-Star break, Wheeler has posted a 2.44 ERA and a 2.26 strikeout-to-walk ratio. His ERA currently ranks forty-third among qualified MLB pitchers. High pitch counts continue to be an issue for Wheeler, however, as he has not pitched more than six-and-two-thirds innings in any of those starts.