The Home Run Derby and Its ‘Carry Over’ Effect

Help us all if one of the home run derby contestants goes on a cold streak. Someone, somewhere, will mention that the slump started right after the player partook in a contest all about hitting the long ball, and naturally hasn’t adjusted his mechanics or mindset since. The poster boy for the post-derby slump is Bobby Abreu. He hit a of homers in the first half, only a few in the second, yet still wound up with around what you would expect from a slugger on the wrong side of 30.

Any fears of a powerless second half because of the derby are extinguished when you examine the last three seasons of participants. Taking all 24 of their first and second half homerun and plate appearances, I found that the difference is marginal, and can probably be attributed to regression more so than anything derby related.

First half HR/PA%: 5.52
Second half HR/PA%: 4.79

Over the average second half (377 plate appearances) the difference is 3 home runs. You could blame this on a meaningless competition, or you could chock it up to regression. Why are these guys even chosen for the event? Because A) they’ve hit a ton of homers in the first half or B) they’ve hit a ton of homers in the past. “A” is the key to the regression pie. Let’s take a look at the biggest drops.

Justin Morneau (2007) 6.6% /2.3%
Dan Uggla (2008) 6.6%/3.3%
Chase Utley (2008) 6%/2.8%
David Wright (2006) 5.2%/2.2%
Lance Berkman (2008) 5.5%/2.6%

Each of these guys outdoing their previous numbers and the league’s numbers; a combination which signals some regression is on the way. That means, it’s not a physical or mental adjustment some players are going through, but rather a statistical one.




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9 Responses to “The Home Run Derby and Its ‘Carry Over’ Effect”

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  1. Ryan says:

    Utley’s hip injury probably had more to do with his drop off in HRs than the derby.

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  2. MGL says:

    As I mentioned on my blog, none of the announcers tonight could figure that out (that HR derby participants are chosen because they got lucky in the first half), as they were droning about how most derby players hit fewer HR in the second half. To their credit, someone said that they doubted there was any cause-effect relationship or some such thing.

    R.J., if you want to present data to the general public, who likely don’t understand regression toward the mean and concept that all the players in the derby likely got lucky in the first half, simply every player in the derby with a player with similar HR totals in the first half who was not in the derby. You will likely find (given a large enough sample size) almost the exact same HR rate in the second half between the control and experimental groups. As I said, this is a nice way to explain this concept, or at least illustrate it, to the layperson or casual fan (or TV commentator I guess).

    Joe Morgan actually – and I kid you not – said this:

    “All players get tired in the second half. That is why very few players hit more HRs in the second half.”

    Check out the % of players who hit more HR in the first or second half. What do you think it would be? Morgan says “very few” players hit more HR in the second half of the season and he should know as he has played and commentated for 40 years or so…

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    • Davidceisen says:

      “All players get tired in the second half. That is why very few players hit more HRs in the second half.”

      I guess Joe doesn’t include pitchers in the category of all players.

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  3. MGL says:

    This sentence:

    “R.J., if you want to present data to the general public, who likely don’t understand regression toward the mean and concept that all the players in the derby likely got lucky in the first half, simply every player in the derby with a player with similar HR totals in the first half who was not in the derby.”

    Should read, of course:

    “R.J., if you want to present data and concepts like this to the general public, who likely don’t understand regression toward the mean and the concept that all the players in the derby likely got lucky in the first half, simply match every player in the derby with a player with similar HR totals in the first half who was not in the derby.”

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  4. Yakker says:

    I’m surprised no one has mentioned that the second “half” typically has approx. 10% fewer games than the first “half.”

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    • Tonio says:

      Seriously, as I was reading these comments I was waiting for someone to make that utterly obvious comment. They SHOULD hit slightly fewer homers, they play slightly fewer GAMES in the second half!

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  5. Ben says:

    I guess I hear the rumors differently; I’ve heard some say that a player’s hitting in general can suffer in the second half (not necessarily power numbers). My counter argument is that a lot of these guys try to bomb home runs in BP, so I don’t see why this would be much different.

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    • Tonio says:

      Agreed, I mean apparently Ichiro has been known to go nutso sometimes and go for homers during the occasional batting practice. This doesn’t seem to effect his ability to hit at all despite the fact that he’s not a HR-hitter.

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  6. brent says:

    I don’t know the numbers, but everyone in Toronto believes it helped tank Alex Rios.

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