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:

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.