Sure, some players have gone into funks after making deep runs in the Derby. But overall, there's just not much evidence to suggest that players who take a lot of swings on Monday night are in danger of significant drop-offs after the All-Star break.
And for what it's worth, the players participating in the event don't think there's much of an effect either.
"I don't think so," said the Mets' David Wright, eliminated in the first round on Monday. "It's three rounds of BP. ... But I think it's just a myth that it kind of messes with your swing."
There have been injuries, and that can certainly diminish a player's performance. One who comes to mind is Jim Edmonds, who aggravated a shoulder injury in the 2003 Derby. But those have been rare occurrences.
Overall, the data suggest that even for players who take a lot of swings in the Home Run Derby, if there's a hangover effect, it's slight.
The current three-round format dates back to 1995. Over those 18 seasons, 43 players either made the finals or hit a total of at least 15 homers in the Derby. And while their performances fell off slightly in the second half, it wasn't drastic.
Those 43 players, on average, posted a .305 batting average, .399 on-base percentage, and .586 slugging percentage in the first halves of the seasons where they appeared in the Derby. In the second half, their average line was .298/.397/.570. (Those numbers exclude Jose Bautista, who played only six games in the second half in 2012 because of an injury).
Put another way, 16 players saw their performance improve in the second half, as measured by OPS. Twenty-five saw their OPS fall in the second half. One, Miguel Cabrera, managed exactly the same, while again Bautista is excluded.
So there is admittedly a slight drop-off, particularly in power. But there's also a selection effect in play here. Players chosen for the Derby are, in many cases, players who have big first halves -- think of guys like the Orioles' Chris Davis and the Pirates' Pedro Alvarez in 2013.
Simple logic suggests that when a player has a half-season at that kind of staggering level, he's going to experience some correction in the second half. It needn't have anything to do with the Derby; it's just hard to keep up a career-best level for a full six months.
If there is an effect, it appears to happen more in the short term than the long. Players who went deep in the Derby saw more of a drop-off in their first 10 games after the break than in the second half as a whole.
The average batting line for the 43 players in their first 10 games of the second half was .285/.386/.536, a bigger drop-off than in the second half as a whole.
Yet even this could be due to another effect. Players who participate in the Derby often feel like they don't really have any down time during the All-Star break. They're busy the whole time, rather than getting more of a breather.
Additionally, there are some interesting numbers to break out within the first-10-games data. Plenty of players have gone deep in the Derby more than once, and some of those players have had both good and bad starts after the break.
Sammy Sosa, for example, struggled mightily after a long Derby run in 2002, hitting .171 and slugging .257 in his first 10 games of the second half. But in 2000, he roared out of the break with a .410/.489/.897 line. Likewise for Ken Griffey Jr., who came out slow in 1999 and 2000 but torrid in 1998.
Prince Fielder has also done each once. Last year, he had a much bigger second half than first. In 2009, he faded a bit in the second half, though that's partly just because he was otherworldly in the first half.
"I kind of swing the same way, kind of, anyway," Fielder cracked. "It really doesn't mess my swing up at all, actually."
So perhaps Harper and Cespedes, Monday night's finalists, will encounter a brief lull after the All-Star break. But they're unlikely to see any real long-term effect on their performance, and there's plenty of precedent for them surging in the second half as well.