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The Home Run Derby doesn't affect some types of hitters more

Overall, the production of Derby hitters does decline in the second half. But are natural pull hitters less susceptible to that kind of decline?

Bryce Harper has the lowest Pull% and highest Oppo% of any hitter to participate in the Derby in the last five years. But even Harper saw his wOBA drop 24 points in the second half after making it to the Derby finals last year.
Bryce Harper has the lowest Pull% and highest Oppo% of any hitter to participate in the Derby in the last five years. But even Harper saw his wOBA drop 24 points in the second half after making it to the Derby finals last year.

There's no such thing as the Home Run Derby affecting a player's performance. At least, that's what others have found: once you filter out the junk, there's no reason to think that participation in the Derby puts a hitter into a tailspin. But on the whole, the production of Derby hitters does decline. It's a little like that kid who happens to turn the light switch off at the exact moment that the power goes out: it feels like there's a connection.

With the Derby, it's more like the connection happens more frequently. But does the kid tend to throw the switch when the power tends to go off anyway? Hitters selected for the Derby tend to have hit particularly well in the first half. Hitters who have hit particularly well in the first half tend to be hitting beyond their talent level. And hitters who have been hitting above their talent level tend to see some kind of dropoff.

In the last five seasons, 40 players have participated in a home run derby (counting repeat performers for each performance). 28 of them have seen a drop in weighted on base average from the first "half" to the second — and some have seen their production shrivel, like Brandon Inge in 2009, Jose Bautista in 2011, Matt Kemp and Mark Trumbo in 2012, and Chris Davis last season. Each dropped around .100 points of wOBA from first half to second, a little like turning Joe Mauer into Dan Uggla at the plate.

There really aren't any examples of the reverse phenomenon — the largest wOBA jump in the last five seasons was Prince Fielder last year, who nudged his .373 wOBA to a .428 mark (.055 points). That's probably to be expected, as a majority of Derby participants were playing out of their minds in the first half of the relevant season, and there wasn't much ground to gain. Just three Derby participants in the last five years had a first-half wOBA under .348 (all three came last year: Yoenis Cespedes at .308, David Wright at .304, and Robinson Cano at .302).

Avg First-Half wOBA Avg Second-Half wOBA Difference in Avg wOBA
.396 .364 .032

So there's a difference, on the whole, and it's a significant one. But as Derek Carty suggested at Hardball Times some time ago, the better test may be to compare second-half wOBA to a projection. I'll note as he did that a mid-season projection would be best. But pre-season Marcels still work extremely well:

Avg Second-Half wOBA Avg Pre-season Marcel wOBA Difference in Avg wOBA
.364 .362 .002

I think you're getting the point. Yes, many players decline after Derby participation. But it doesn't seem to be connected; if we picked teams for the Derby and then didn't hold it, we might expect the exact same decline in performance. When trying to predict which of this year's Derby participants will suffer through a decline, then, you need not look any further than their current production and the most recent projections. That's what the projections are for.

We keep hearing, though, that players whose swings aren't built for home runs are particularly susceptible to getting out of whack because of a Derby. Is that true? Albert Pujols and Joe Mauer suffered wOBA drops in 2009 (.046 and .027, respectively), and other hitters who aren't necessarily thought of as power-first guys have made up a pretty big chunk of the group of 40.

Taking the leap that power-first guys are also pull-first guys, I computed the percentage of the time that each of the 40 Derby participants hit the ball to their pull field ("Pull%"), as well as the percentage of the time that they batted the ball to the opposite field ("Oppo%").

The results: there's no evidence to suggest that all-fields hitters are more susceptible to a post-Derby slump than pull hitters. In fact, Pull% and drop in wOBA (first half to second) shows a slight positive correlation (.247). That suggests that, if anything, it's pull hitters who may be more likely to be ravaged by a post-Derby storm.

1st-2nd and Pull% 1st-2nd and Oppo% Marcel-2nd and Pull% Marcel-2nd and Oppo%
.247 -.268 .166 -.200

Why do both Pull% and Oppo%? I wanted to see if hitting the ball up the middle had anything to do with it. But there you have it: almost no relationship between spray and post-Derby slumps. In some small respect, the more frequently you hit the ball to your pull field, the greater a drop in production you can expect, regardless of whether you're comparing first half and second half wOBA or Marcels and second half. And the more frequently you hit the ball to the opposite field, the less likely you're going to see your production take a dive.

There isn't much here: the sample size is still very small, and chances are that even the little relationship we see here has only to do with the quality of hitter. Better hitters may both pull the ball less and be less likely to see even a random drop in production. But please, don't tell me again that guys like Mauer, Wright and Paul Goldschmidt should pass on the Derby because they're more likely to be harmed by changing their swings.

. . .

All statistics courtesy of FanGraphs. Many thanks to Jeff Sackmann and Tom Tango for making the Marcel projection data public, and to Baseball Heat Maps for making the database available.

Ryan P. Morrison is a featured writer at Beyond the Box Score, and co-author of Inside the 'Zona, a site on the Arizona Diamondbacks with a sabermetrics slant. You can follow him on Twitter: @InsidetheZona.