Let’s start with the heater, which Wheeler uses the most out of his five-pitch arsenal.
Wheeler’s fastball usage dipped to a career-low 30 percent in 2019 and is up to 45.7 percent in 2021. He’s using his fastball more often this season than he has since he threw it 54.3 percent of the time over 100 innings as a rookie in 2013.
Throwing his heater more often is working. Opponents are batting .222 with 37 strikeouts and only seven extra-base hits against Wheeler’s four-seam fastball, which ranks seventh in average velocity among qualifiers.
When I started my research for this piece, I thought an increase in fastball velocity might be a major reason for Wheeler’s high strikeout rate. But that doesn’t look like it’s the case.
Phillies RHP Zack Wheeler: 4-Seam Fastball Velocity, 2019-2021
- 2019: 96.7 (94th percentile)
- 2020: 96.8 (95th)
- 2021: 97.2 (95th)
Wheeler ranked in the 90th percentile or higher in fastball velocity every season since 2018 and has been in the 94th percentile or better each of the last three seasons. His fastball velocity has improved each year of the Statcast era, but not enough to point to increased velocity as a main reason for more strikeouts.
One thing that stood out to me during my research was that Wheeler and Rays starter Tyler Glasnow both ranked in the 95th percentile in average fastball velocity in 2020, but Glasnow’s strikeout rate ranked in the 97th percentile, while Wheeler’s ranked in the 18th.
It’s clear that factors other than velocity are responsible for Wheeler’s increase in strikeouts.