Beware of the Power-Surge Imposters!

It’s no secret that power is up in baseball. While guys like Brian Dozier are hitting their 40th home run and Tyler Naquin are putting up Barry Bonds-type numbers against breaking and offspeed pitches, investigations into the potential of a juiced ball have persisted throughout the analytical community. We can’t say for sure why power is up, but it is. The league’s .167 isolated slugging percentage is the highest the peak of the steroid era in 2000, and the second-highest in the history of the game, and the 14-point increase in ISO from 2015-16 is the 10th-largest single-season in increase since the modern era began in 1921.

Such a sudden and drastic increase can make it difficult to contextualize player changes on the fly. When I wrote about Eric Hosmer’s season two weeks ago, this line from a comment by user “isavage” stuck with me:

It doesn’t seem like Hosmer’s performance has fluctuated too greatly, it’s more that his offense didn’t get better when the league’s offense got better.

It’s not entirely true — Hosmer is striking out more and performing more poorly on balls in play relative to last season. But he does have a point. Royals fans might look at Hosmer’s seemingly increased power — a career-high 23 home runs, up five from last year, and a 14-point boost in ISO — and draw a silver lining that at least Hosmer is finding more power in his stroke. Except, it’s not true. Hosmer’s power, relative to the league, has actually dropped this season. He’s just a power-surge imposter.

I was interested in finding more power-surge imposters, so I grabbed two spreadsheets with every player who batted at least 300 times in each of the last two seasons. I league-adjusted everyone’s ISOs, and I did a rough park-adjustment estimate using our home-run adjustment, too. Then, I filtered for every player who’s seen an increase in raw ISO, but a decrease in adjusted ISO.

Be careful, folks. We’ve got 19 power-surge imposters on our hands:

The Power-Surge Imposters, 2015-16
Name 15 ISO 15 ISO+ 16 ISO 16 ISO+ ISO DIF ISO+ DIF
Chris Carter .228 142 .263 139 .035 -3
Pedro Alvarez .227 163 .253 139 .026 -24
Ian Desmond .151 102 .176 100 .025 -2
Yoenis Cespedes .251 166 .274 162 .023 -3
Asdrubal Cabrera .164 111 .187 111 .023 -1
Brett Lawrie .148 104 .165 91 .017 -13
Matt Carpenter .233 161 .247 157 .014 -5
Eric Hosmer .162 113 .176 113 .014 -1
Kendrys Morales .195 136 .205 131 .010 -5
Dexter Fowler .161 103 .169 99 .008 -4
Mitch Moreland .204 127 .211 120 .007 -7
Brandon Guyer .148 101 .154 95 .006 -6
Odubel Herrera .121 74 .126 70 .005 -3
Eugenio Suarez .167 95 .172 90 .005 -5
Howie Kendrick .114 73 .118 69 .004 -4
Joe Panik .144 109 .147 102 .003 -7
Martin Prado .106 78 .108 72 .002 -5
Josh Harrison .103 74 .105 69 .002 -5
Chase Utley .131 80 .133 78 .002 -2
ISO: isolated slugging percentage
ISO+: isolated slugging percentage, adjusted for league and park

We find Hosmer in the eighth row of our spreadsheet there, alongside teammate Kendrys Morales, whose 10-point ISO increase is also nothing but a mirage.

The top six names on the list are mostly the result of a park change, the best example of this being Pedro Alvarez, who sticks out like a sore thumb as our No. 1 power-surge imposter. Last season, Alvarez ran a .220 ISO while playing his home games in the spacious PNC Park, the third-most home-run suppressant ballpark in baseball. This year, he’s boosted his raw ISO by a whopping 26 points. He’s also gone from the third-worst homer park to the fifth-best homer park in Camden Yards, while playing in a more power-happy environment overall. Voila! That 163 ISO+ last year is actually just a 139 ISO+ this year.

Going a step further, one might point to Alvarez’s average exit velocity, up to 94.0 mph this year from 92.7 last year, as a sign that he is, in fact, hitting the ball harder, contrary to his 34-point drop in ISO+. However! Correlating with the league-wide increase in power production is, of course, a league-wide increase in exit velocity by a little more than half a mile per hour. That makes up half of Alvarez’s exit velocity boost. Then, work done by Jonathan Judge, Nick Wheatley-Schaller, and Sean O’Rourke at Baseball Prospectus led to park adjustments for exit velocity, while controlling for pitcher and batter, which found that Camden Yards, Alvarez’s home park, inflates exit velocity by nearly a full mile per hour, while PNC Park, his previous home, is closer to neutral. These two adjustments now more than make up for his perceived increase, leading us to a similar conclusion as the one found in the preceding paragraph — that the power increase exhibited by Alvarez on the surface is simply a delusion.

Which is particularly interesting in this case, because Alvarez was somewhat surprisingly non-tendered by the Pirates this offseason after they were not able to find a trade partner for him. Alvarez agreed to a one-year, $5.75-million deal with the Orioles, hoping for it to serve as something like a pillow contract while he rebuilt his value. By some of the raw figures that best measure Alvarez’s strength, he might’ve done exactly that during his time in Baltimore. Dig a bit deeper, though, and we find that not only is Alvarez really no better off than he was before being non-tendered last season, he might have actually taken a step back.

More cases like Hosmer’s — where the imposter label is simply a product of the changing batted-ball environment and not a change in home park — exist, too. Like Matt Carpenter, who’s seen his ISO+ drop by five points, despite a 14-point boost in raw ISO, or Dexter Fowler, whose eight-point ISO increase is actually a four-point ISO+ decrease. These aren’t monumental changes; you’re probably not looking at Carpenter’s season any different now than you were before you read this post. But they’re real, and this all can help serve as a reminder that every number ought to be viewed in the context of those around it, similar to Neil Weinberg’s recent piece on how the home-run spike has fooled managers. Don’t be like those managers who were fooled. Don’t get trapped by the power-surge imposters.

August used to cover the Indians for MLB and, but now he's here and thinks writing these in the third person is weird. So you can reach me on Twitter @AugustFG_ or e-mail at

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6 years ago

A more tightly wound ball is the simplest, easiest answer. It may not be the correct one, but it seems like the answer until someone finds a better one.

Slacker Georgemember
6 years ago
Reply to  dl80

This is the classic “baseball of the gaps” fallacy made famous by Henry “Catfish” Drummond.

6 years ago
Reply to  dl80

That’s not an answer. That’s a hypothesis. Until testing proves or disproves it (and proves something else) we don’t have an answer, simple and easy or otherwise.