What is Zack-ening with Wheeler?

What happened in Wheeler's first start and, is it sustainable?

When looking for a way to properly describe Zack Wheeler’s first start of the year, I believe Nick Pollack’s words are perfect: It was beautifulHe pitched seven scoreless innings, allowing just one hit, striking out 10 batters while walking none, against Atlanta. Oh, and he drove in two runs, too. You can check how he retired 23 consecutive Atlanta batters, among other beautiful pitching things, in the following summary:

(courtesy of www.mlb.com)

So, what’s the deal with Wheeler? Let’s try to find out, first, looking at his career numbers:

Wheeler missed time between 2015 and 2017 due to Tommy John Surgery and right arm stress reaction, but, outside of that, he’s been an innings machine, averaging 187.2 IP during his full, healthy seasons.

His career win-loss record is 49-40, with a career 3.67 ERA, 1.27 WHIP, 14.4 K-BB%, and a 26.4 CSW%; not overly-enthusiastic numbers, to be honest, but far from terrible.

During the 2020 sprint season, in the 11 games he started, Wheeler had the lowest FIP and ERA of his career, at 3.22 and 2.92 respectively, showing flashes of fantastic pitching in a more consistent way. This made Wheeler move a little up from 115 to 99 ADP, according to NFBC Draft Champions drafts from 2020 and 2021; that’s middle-of-the-pack, 35th-ish pitcher off the board in ADP.

So, what happened for Wheeler in this first 2021 start that made him a more dominant pitcher?

To try to answer this we need to check his recent outings, and that means the only one this regular season but also those from Spring Training, this amounts to six starts in ST and the one from last Saturday, 28 IP total. It’s a small sample, so let’s proceed with caution.

Zack Wheeler’s 4-Seamer Avg (MPH) by year:

The first thing we usually check is velocity, of course. In this regard, Wheeler’s 4-Seamer is at the top of his game, averaging almost 97 mph since 2019. He uses it a bit more than 40% of the time and, in the first start, he threw it 38 times, getting a 38.1 Whiff% and a 35.7 PutAway%, both very good.

Fastball? Check.

Zack Wheeler’s xwOBA-wOBA (the lower, the better):

A good quick way of checking how a pitcher is getting “touched” by batters, the overall quality of the contact he is allowing, is via xwOBA as it uses a combination of exit velocity, launch angle, and, on certain types of batted balls, sprint speed. xwOBA is more indicative of a player’s skill than regular wOBA, as xwOBA removes defense from the equation. Hitters, and likewise pitchers, are able to influence exit velocity and launch angle but have no control over what happens to a batted ball once it is put into play.

Furthermore, subtracting wOBA from xwOBA gives us have an idea of how things could’ve been if fielding would have not played a part; isolating more the pitching itself, rather than the team and environment around him. In this regard, the jump in 2021 has been dramatic for Wheeler, meaning that he is limiting the quality of contact more than ever before.

xwOBA-wOBA? Check.

These stats are good first ingredients in a recipe for success, but we are still missing the main constituents of Wheeler’s great start:

Zack Wheeler’s K-BB% & CSW% by year:

(** Spring Training and Regular Season combined.)

Here is where the early leap taken by Wheeler is impacting his game the most; he’s never struck out batters at this rate, nor induced called strikes and whiffs like this. That’s as important as it comes. In fact, these stats have always been underwhelming for him, one of the reasons he has not been able to take a step forward.


A Tale of Two Zacks


Even though Wheeler has a very respectable four-seamer, he’s never been able to have a good K%, but he has survived on two key metrics: Zone% and O-Swing%. Last season, he was 17th in Zone% + O-Swing% with 79%, trailing the leader Sixto Sánchez, at 82.7%, only by 3.7 percentage points. If we combine the 2019 and 2020 seasons, Wheeler jumps to sixth place with 79.55%, trailing only control freaks like Kyle Hendricks, Yu Darvish, Charlie Morton, Ryan Yarbrough, and Gerrit Cole, by less than 1 percentage point.

Wheeler’s elite command and control have made him good enough, but his inability to get strikeouts has kept him from moving beyond that. When measured by speX:

2019-2020 speX Leaderboard

Highlighted in green are the top 3 for each stat on the board, in red the worst three; this way, it’s easy to see what’s keeping Wheeler from climbing on the board. Or better said, was keeping.

If we keep the rest of the values and recalculate speX with the recent K-BB% and CSW% values, this is how the same board would look like:

2019-2020 speX Leaderboard (modified)

Improvements in K-BB% and CSW% make all the difference in the world, as Wheeler jumps 20 places from 39th to 19th, in the close company of elite pitchers like Aaron Nola and Clayton Kershaw. That’s huge.

The pressing question here is, what’s driving this premature newfound success?

While digging into it, it’s not easy to pinpoint one specific thing as the key for the early good results but, it is important to acknowledge that Wheeler has been trying since spring training to get ahead of the batters, and it looks like it’s working: since 2019, this season (including ST) it’s the first time he gets a strike more than half of the times, at 52%, when the count is even; that’s top ten for pitchers with at least 100 pitches (including ST) for this season.

The other important question is, how sustainable is this from now on?

This is a really hard question to answer but based on the assumption that strike-related metrics are some of the fastest to stabilize, we could have a good probability that the upward trend in K-BB% and CSW% displayed by Wheeler this year (adding Spring Training for added sample-size) will continue, and if that holds, we are in for a stupendous season from him.

Although I am no fan of anecdotal evidence, I will also like to add the following info shared by notable high stakes fantasy baseball player, Phil Dussault in his Twitter handle which I find very interesting:

There might be a lot of survivor bias here, as the best pitchers are intrinsically expected to take the first turn in the rotation, but I like the fact that Wheeler’s numbers in his first regular-season game are backed up by strong Spring Training innings. The sample size is not ideal, but it is a lot better than just a single game.

Bottom line, signs are pointing to a substantial improvement in Wheeler’s ability to get strikes and that’s what is fuelling this important new-found way of getting batters out. While it is still too early to be totally sure about how will this work for the rest of the season, I believe that there is a good probability that it will continue.

Photo by Kyle Ross/Icon Sportswire

Carlos Marcano

Just a Venezuelan, not living in Venezuela. Intrigued by most of the things that can be measured in baseball, football, basketball, soccer, and life. I love to try to estimate performances.

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