The Wheel of Fate: What’s behind Wheeler’s ERA?

Saying that someone is having a quiet season is not typically taken as a compliment. Perhaps this isn’t quite so for pitchers, for whom a lack of attention can indicate that they’re quietly taking care of business, not giving their opponents much to celebrate or their own team’s fans much reason to reach for the antacids. Still, while quiet efficiency is perfectly acceptable for most starters, you’d like your aces to give you something to write home about. Zack Wheeler usually does.

But not so this season. Wheeler currently has a solid but unspectacular ERA of 3.88, and remains in a sort of no man’s land: not pitching poorly by any measure, but not always throwing the gems that would draw accolades (although his last outing, a 7-inning, 1-run performance against the Guardians, looked like the Wheeler we’re used to). He has done his job with reasonable effectiveness, but the ERA remains something of a sticking point for fans browsing the statistics with their morning coffee. A somewhat pedestrian ERA for a pitcher who is typically anything but? What’s happening with Wheeler?

Understanding what an ERA means, or doesn’t mean, requires taking a bit of a deeper look under the hood. An individual ERA tells a story, but perhaps not the story. Wheeler’s 3.88 ERA is substantially worse than the ERAs he put up in the past 2 seasons (2.82 and 2.78), but does this really mean he’s pitched worse this season? His strikeout percentage of 27.1% is a tad better than what he put up last year, and slightly worse than the 29.1% mark he achieved in 2021. He’s walking fewer batters than he usually does; his clip of 4.6% places him in the top 10% of the league, and, should it hold, would be the best of his career. The pitches his opponents aren’t hitting aren’t a problem.

What about the pitches they do hit? Opposing batters are barreling the ball 5.4% of the time against Wheeler; a mark that’s a bit more than 2 percentage points better than the number he put up last year, although a bit worse than his mark in 2021 (4.6%). Conversely, batters are getting hard hits off him somewhat more often than they have in the past, with 37.5% of hits against him this year qualifying, as opposed to 34.5% in 2022 and 28.5% in 2021. That increase in hard hits allowed is surely contributing to the elevated ERA to some degree, but it doesn’t seem likely to be the main explanation.

There’s also the matter of what pitches he’s throwing. Like so many pitchers, Wheeler has introduced a sweeper into his pitch mix this year (Statcast records him as having thrown it 3 times in 2022, though there’s a possibility that those were misclassified). He throws it 11.8% of the time. That has come mostly at the expense of his slider (thrown 17.1% of the time this year vs. 26.8% of the time in 2022). Wheeler’s changeup, which has been falling out of his favor for the past few seasons, is seemingly extinct; he’s thrown it only once in 2023. His usage of his fastball, curveball, and sinker has, to date, remained steady since the 2021 season.

A major change in pitch mix could explain a change in results, and a major change is precisely what Wheeler made when he added the sweeper. But Wheeler’s sweeper has been quite effective, inducing a higher percentage of whiffs (42.7%) than any of his other pitches, and producing a lower batting average (.189) than any of the others too. The addition of a highly effective and frequently used pitch to his arsenal certainly won’t explain a rise in ERA. A decline in effectiveness of his preexisting pitches would explain it, but this doesn’t seem to be the case either. The batting average against his sinker is a bit higher in 2023 (.294) than in 2022 or 2021 (.238, .253), and the same is true for his slider (.253 this year, .204 in 2022, .196 in 2021). But the velocity, spin rate, and break, both vertical and horizontal, for all of his pitches this year is consistent with where it’s been in the past few seasons. He doesn’t seem to be losing his stuff. So what, then, explains the ERA?

Wheeler’s ERA is 3.88, but his Expected ERA (xERA) is 3.27, and his FIP is 2.88. xERA and FIP are different measurements, but both can be thought of (albeit in a simplified sense) of measuring luck or lack thereof for a pitcher. If a pitcher’s actual ERA is well above his xERA or FIP, bad luck may be to blame, though it’s not the only possible explanation. This being the case for Wheeler, his 2023 may look worse than it really is. Luck, the vagaries of the art of fielding (along with the fact that some of the Phillies’ starting 9 are not, it must be said, known for their prowess in that category), and the smaller sample size of a yet to be completed season seem more likely than any genuine drop in effectiveness.

This may be cold comfort for Phillies fans who expect, as all fanbases do, a string of uninterrupted ace-ness (for lack of a better word) from their best pitchers. Still, there is no reason for panic. Wheeler is on the bump tomorrow against Pittsburgh. Perhaps he picks up right where he left off after 7 innings of 1-run ball in his last start, and never looks back. Perhaps it’ll take a bit longer. Either way, he’s very likely to look like himself again soon.