Philadelphia Phillies right-hander Zack Wheeler has been one of the best starting pitchers in Major League Baseball this season. He owns a 2.52 ERA, 155 ERA+, and 2.46 FIP through 11 starts — the same number of starts he made in the pandemic-shortened 2020 season. His 2.9 WAR is tied-for-sixth in the majors and fifth among pitchers.
Fresh off three straight double-digit strikeout games — including a career-high 14 against the Tampa Bay Rays on Saturday — Wheeler ranks third in the National League with 92 strikeouts and is sixth in the NL with an 11.04 K/9 ratio.
If he was pitching like this in a contract year, he’d likely get north of a $30 million average annual value in free agency. He’s been the Phillies’ most valuable player in the second of a five-year deal as continues to rise from an above-average No. 2 starter to a legitimate ace.
Ben Clemens of FanGraphs recently went in-depth on how the 30-year-old has quietly improved this season. The biggest difference for Wheeler, Clemens explains, is his career-high strikeout rate that stems largely from a more effective use of his pitch arsenal — especially when he gets two strikes on batters.
Wheeler has always had strikeout stuff, but he’s never been a “strikeout pitcher”…until this season.
2019: 23.6% (58th percentile)
2020: 18.4% (18th)
2021: 31.7% (85th)
Wheeler’s 18.4 percent strikeout rate in 2020 ranked just 49th among qualified starting pitchers while his 31.7 percent mark so far in 2021 ranks 11th in the majors. Wheeler’s strikeout percentage increase of 13.3 percentage points is the fourth-highest jump among all qualified pitchers this season and the highest jump among active starting pitchers.
Wheeler’s strikeout rate jump from the 18th percentile in 2020 to 85th in 2021 is even more impressive — considering his previous career-best ranking in the Statcast era (2015-present) was in the 61st percentile (2018).
His whiff percentage (overall swings and misses) is up as well, to a career-high 27.7 percent, after it sat between 21.8 and 24.5 from 2017-2020.
Wheeler uses all five of his pitches — fastball, sinker, slider, curveball, changeup — to get strikeouts. Looking at how often he throws each pitch gives us some insight into how he’s drastically improved his strikeout rate.
Wheeler started using his fastball a lot more last season — his first with the Phillies — and has continued to rely on it in 2021. His slider usage is up significantly and his curveball, despite a lower usage rate this season, has arguably been his best pitch (more on that later).
Wheeler has cut his sinker use almost in half — nearing a career-low rate — since he left the Mets and he doesn’t use his change-up much, so we’ll focus on his other three pitches for this piece.
Zack Wheeler #45 of the Philadelphia Phillies Photo by Mitchell Leff/Getty Images) /
Let’s start with the heater, which Wheeler uses the most out of his five-pitch arsenal.
Fastball
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.
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.
Zack Wheeler #45 of the Philadelphia Phillies (Photo by Tim Nwachukwu/Getty Images) /
Two nasty breaking balls — including one that he is using more than he ever has — are part of Phillies right-handed starting pitcher Zack Wheeler‘s success.
Slider
Wheeler is throwing his slider about one-quarter (25.6) percent of the time this year, a big change from his approach in the pandemic-shortened 2020 season — when he threw it only 15.9 percent of the time. It’s also a significant increase from his previous career-high 20.3 percent use of the pitch from 2017.
The slider has become a pitch that Wheeler trusts and can consistently fool hitters with, specifically those who bat left-handed. Wheeler has thrown 285 sliders this season and nearly 200 (194) of them have been to lefties.
Overall, opponents have a .159 batting average (10-for-63) with 27 strikeouts against Wheeler’s slider. The pitch also has a 32.9 percent whiff rate and a 31.8 percent putaway rate, which ranks 10th in the majors on sliders.
In addition to how often he throws it, velocity and spin are also important when it comes to the right-handed pitcher’s slider. At 91.2 miles per hour, Wheeler has the second-highest average slider velocity in Major League Baseball — behind only his former New York Mets teammate and perennial Cy Young Award candidate Jacob deGrom (91.6 miles per hour).
The active spin percentage is up on four of Wheeler’s five pitches. Also, his jump from 27 percent active spin on his slider in 2020 to 39 percent in 2021 is by far the biggest spin increase in his arsenal.
Phillies right-handed starting pitcher Zack Wheeler’s slider has been great, but his curveball has been even better, despite a much lower usage rate.
Curveball
Wheeler is not throwing his curveball much this season — just 88 times through 11 starts — but yet it is nearly unhittable when he does throw it. He is excelling in three notable categories, shown below, with his Major League rank among pitchers who have thrown at least 50 curveballs this season in parentheses.
Put Away %: 38.5% (1st)
Strikeout %: 55.6% (T-2nd)
Whiff %: 51.3% (5th)
Wheeler throws his curve only eight times per game on average, so it is clear that he’s picking his spots extremely well; it’s the definition of a “put-away pitch.” He leads all pitchers in curveball putaway percentage, he has an exceptional strikeout rate with the pitch, and he’s generating swings and misses more than half the time he throws the deuce.
It is no surprise that opponents are hitting .125 (3-for-24) with 15 strikeouts and zero extra-base hits against Wheeler’s curveball, and the expected stats against his curve further prove how dominant that pitch has been.
xBA: .111 (4th)
xSLG: .171 (T-5th)
xwOBA: .159 (5th)
Translation: Wheeler’s curve is elite. It is extremely tough to hit now and the predictive trends show it is not getting easier any time soon.
All-Star voting opened up on Thursday. If there is any season in which Wheeler deserves his first career nod to the Midsummer Classic, it surely should be 2021.
Good luck, hitters.
*All stats updated through games played on Monday, May 31
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