This article was written by Marcus Jaiclin - Joseph McCollum

This article was published in the Fall 2010 Baseball Research Journal

Analyzing whether players who participate in the Home Run Derby see their performance suffer in the second half.



Analyzing whether players who participate in the Home Run Derby see their performance suffer in the second half. A variety of sources have indicated the existence of a Home Run Derby curse. For example, Alex Rodriguez has been quoted as saying about the Derby, “I try to stay away from that” and “My responsibility is to the New York Yankees. I need my swing to be at its best.”[fn]Mark Feinsand, “A-Rod to Skip HR Derby, Claims It Tampers with Swing,” New York Daily News, 30 June 2008.[/fn] The implication is that participation in the Derby would leave his swing somewhere other than at its best. In the Wall Street Journal, we read that “for each of the past four years, one player who has hit at least 10 home runs in the Derby has seen his power disappear once play resumed for the second half of the season.”[fn]Dave Cameron, “The Mysterious Curse of the Home Run Derby,” Wall Street Journal, 13 July 2009.[/fn] We also see on mlb.com that the curse is real “at least since 1999” and that “43 out of 74 players saw a decrease in their production after the Derby.”[fn]“The HR Derby Curse Is Real!” mlb.com, fantasy411.mlblogs.com/archives/2008/07/the_hr_derby_curse_ is_real.html[/fn]

Hardball Times came out with the opposite perspective: “No matter how long a hitter lasts or how many home runs he hits, we still don’t see any signs of a second-half decline.”[fn]Derek Carty, “Do Hitters Decline After the Home Run Derby?” Hardball Times, 13 July 2009.[/fn] However, the list of caveats to their analysis was almost as long as their analysis, which might lead to some skepticism.

We hope to put this subject to rest with some clear assumptions and a careful consideration from multiple perspectives.

WHAT IS A HOME RUN DERBY CURSE?

The goal of this analysis is to determine if the claim of a Home Run Derby curse is borne out by the performance of the players who participated. In order to do so, we need to determine how the idea of a Home Run Derby Curse should be interpreted statistically.

Interpretation 1

A player who participates in the Home Run Derby experiences a decrease in offensive and power hitting statistics in the second half, as compared to the first half of that season.

Interpretation 2

A player who participates in the Home Run Derby experiences a decrease in offensive and power hitting statistics in the second half, as compared to his usual production.

Behind the first interpretation is the assumption that a player would have continued to perform at the same level for the rest of the season had he not participated in the Derby. There is certainly some reason to believe that this is true—the player is clearly capable of performing at this level, having done so for half of a season. However, if this level is substantially above his typical level, it may be unreasonable to expect this to continue for the full 162 games. So it seems that this interpretation would tend to predict for the second half a level of performance that is higher than one should reasonably expect.

Behind the second interpretation is the assumption that a player’s career statistics are more indicative of his likely performance than is his first half of the season. Players selected to participate in the Derby are those leading the league in power hitting in the first half of the season and so are, for all except the best of players, performing at a level above their average statistics. Similarly, participants in the Derby are often having an excellent season at the peak of their careers, so a somewhat higher level of performance is to be expected again in the second half of the season. So it seems that this interpretation would tend to predict a level of performance in the second half that is lower than one should reasonably expect.

Neither interpretation is perfect, so we will consider both comparisons, looking at the difference between the post-Derby statistics and pre-Derby statistics, and then at the post-Derby statistics and the players’ usual statistics. In addition, we will consider a third comparison, where we will build a comparable dataset to estimate the expected regression to the mean and to see if a similar effect can be found in a dataset where the actual participation in the Derby is not present as a variable.

ANALYSIS 1: ON ALL PARTICIPANTS IN THE HOME RUN DERBY

In our first pass through the data, for each player who ever participated in the Home Run Derby, we collected all of his statistics for all seasons, separating any seasons where he participated in the Home Run Derby from any seasons where he did not participate. We restricted the seasons to those where the player reached a total of 502 plate appearances, in order to exclude any unusual averages for a player. The total number of player-seasons in the data is 1,111 (up to and including the 2009 season), 192 of which were seasons where a player participated in the Derby. There were six player-seasons where a player participated in the Derby and did not reach 502 plate appearances, and so those were excluded. This number is small enough to give some indication that participation in the Derby may not be linked to injury in the second half, though the number of occurrences of this is too small to allow us to perform any statistical inference process.

In order to simplify the analysis, we have focused on two offensive statistics: OPS and the percentage of plate appearances that were home runs. We found similar results with other statistics, so the analysis does not depend substantially on this choice. Note that these players averaged 10 to 15 fewer games played after the All-Star Break than before (due to its timing in the schedule more than their own playing time), so only statistics that are computed per at-bat, per plate appearance, or per game would make sense in these comparisons.