What's wrong with Zack Wheeler? Phillies star is struggling at the worst time

A bit of an under-the-hood look at how I put this type of article together: when I hear that some player is struggling, in this case Philadelphia Phillies ace Zack Wheeler, I first go investigate their monthly splits, easily viewable for every player on Baseball Savant. They also have pre and post-All-Star splits and … oh no. Oh no no no.

Wheeler got shelled last night by the Seattle Mariners, giving up eight earned runs in four innings, striking out four but walking five batters. He also was battered with four home runs, sending his counting stats even further into the stratosphere. Something is definitely wrong here.

Zack Wheeler has been struggling hard since the All-Star break

Even before that disasterclass, I knew Wheeler was struggling, but when I checked out his splits I was shaken to the bone. Every single number we use to measure baseball performance has flipped dramatically against Wheeler in his seven starts since the All-Star break. In his first 15 outings, he was 10-1 with a 2.13 ERA. In the seven since the break? 0-4 with a 7.18 ERA. 

So what’s the story here? Has Wheeler just lost it? Has his injury which kept him out until the end of April caught up with him? Fatigue? Let’s just ask some people who were actually at the game, starting with Wheeler himself:

“To be totally honest with you, I feel perfectly fine … healthy, strong,” Wheeler said after the game. “Everything’s there. I don't know. Just got to zone it back in and figure it out.” 

So that’s not super helpful. JT Realmuto suggested that Wheeler is missing on some pitches that he’s trying to place and leaving some things over the heart of the zone. Cal Raleigh (who hit three home runs in that game) suggested a similar situation, saying they were looking for stuff left in the middle of the zone. Wheeler himself lightly suggested the Mariners may have figured out something he was doing to tip his pitches, but we obviously don’t know that for sure.

Wheeler's issues are not easily explained

I’m more interested in the larger trend of Wheeler’s struggles, which is a pretty jarring seven-game sample. I’d love to say this is just one bad start, but Wheeler has strung together a number of concerning outings in a row chock full of home runs and walks. Before the All-Star Break (15 starts) Wheeler gave up 10 total home runs on a problematically low HR/fly ball ratio. Since the All-Star break, that number has stabilized brutally for Wheeler, having given up nine in only 1/3rd as many innings.

Realmuto’s suggestion that Wheeler is leaving stuff over the middle of the plate may have been true last night, but it isn’t broadly true during these last seven starts. In fact, much as I might have wanted to include several charts of Wheeler’s pitch command/plate discipline numbers because man do I love charts, nothing indicated a major shift in his pitch placement. Batters aren’t much better at laying off his pitches, they aren’t really swinging more or making more contact or doing much of anything that tells me Wheeler has somehow lost a step. His velocity isn’t down, his spin rate isn’t down. Wheeler saying, “I feel perfectly fine” actually stands up to the radar gun.

Explaining why he’s suddenly getting launched on could come down to simple statistical regression. He was way below average in home run rate for much of the year, and now the devil has come to collect. It is also distinctly possible that he is tipping pitches, as is occasionally the explanation for this level of carnage, but again: I didn’t find any kind of dramatic plate discipline spike that would suggest that.

Wheeler may just be getting unlucky, and that's a good sign for Phillies fans

The lack of a physical indicator, though, is a good sign for Wheeler that this may just be dumb luck sprinkled with some regression fairy dust. Wheeler’s sub-3.00 ERA never quite matched up with his ERA estimators, and anything FIP-based (basically walks, home runs and strikeouts) was a bit more skeptical of Wheeler’s impact. Turn some of that home run luck around and … yeah.

Honestly, though, I think Wheeler is fine. Think of this like a doctor who has to do all sorts of tests to rule out a serious condition — I feel I’ve ruled out any kind of catastrophic loss of mojo that would be easy to allege after such a rough stretch. Wheeler himself thinks he’s fine, and the pitchers themselves are the best judges of their own quality. He could, of course, be lying, but everything I’ve seen makes me think he’s telling the truth. I suggest patience. 

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