2008 All-Star Game

As you can see, Derby hitters experienced modest declines in batting average, slugging percentage and home-run rate. However, none of those declines can rightly be called drastic or extreme. As well, sample-size issues are at play, and it's possible that a handful of poor second-half performances are skewing the overall numbers.

It's worth noting that over that same span SLGs and home-run rates for all players have slightly increased after the All-Star break. So the decline in power that Derby participants experience is in contrast to the gains that the hitter population at large enjoy in the second half. None of that, though, explains precipitous declines like the ones suffered by Anderson, Abreu, Wright and Rios.

While some of the players seem to believe in the hangover effect, major-league hitting coaches for the most part are skeptical. Jim Skaalen of the Milwaukee Brewers probably speaks for a number of his colleagues when he tells FOXSports.com that concerns about lingering aftereffects are "probably overblown."

Last year, Prince Fielder, one of Skaalen's hitters, competed in the Home Run Derby, and this Ryan Braun is representing Skaalen and the Brewers. Even though Fielder and Braun are young hitters and, presumably, less grounded in their habits than, say, a 10-year veteran might be, Skaalen isn't worried. He saw no change in Fielder's approach after the Derby, and he's not worried about Braun, who, Skaalen says, stays consistent because of his routine. "Major-league hitters can so quickly get back into their swing," says Skaalen. "So it doesn't worry me."

Skaalen also says that the swings he sees in the Derby aren't all that different from the swings he sees on a day-to-day basis. "Maybe a little extra effort to create a bit more loft," he says. "But that's about it."

In fact, Skaalen says the Derby isn't that much different from what power hitters experience during the final round of batting practice before each game — they're getting slower pitches, middle in, and trying to drive them.

So for the most part, taking part in the Derby probably doesn't hurt most hitters. It's an individual question, of course — perhaps some hitters are more prone to coming undone in the mechanical sense — but the statistical evidence that it's a significant and widespread trend is fairly weak. As well, there's the on-the-ground testimony of baseball men like Skaalen. The sensible conclusion is that the hangover effect, in which serious decline is a risk, exists mostly in the imaginations of the hitters.

That's good news for Justin Morneau, this year's Derby champ, and his team, the Minnesota Twins.