Watch out, guys: Being in the Home Run Derby can be dangerous to your stats.
It's been said that the Derby is a "win at your own peril" event because it can affect a player's swing. And the numbers say there may be some truth to that.
The Home Run Derby became an All-Star event at the 1985 game in Minneapolis. As a group, competitors have seen a negative impact on their slugging percentages after the Derby.
Participants averaged a .587 slugging percentage during the first half of their Home Run Derby-winning seasons and a .562 slugging percentage during the second half, a drop of 25 points.
For their careers, the 26 Derby winners averaged a .505 slugging percentage during the first half of the season and a .504 slugging percentage in the second half -- a decrease of only a single point.
Further evidence comes by examining the MLB slugging percentage data during the first and second halves of each season from 1985 to 2012, excluding 1988, when a rainout canceled the Derby.
This comparison enables a wider-ranging look at how slugging percentages fluctuate on average, as not only sluggers are in the sample size, but light-hitting middle infielders, bench bats, MVPs and everything in between. It's also a tremendous sample size -- more than 2.2 million at-bats during the combined first halves of the seasons alone.
But even here, the slugging percentage fell only four points, from .741 in the first half to .737 in the second half.
So why waffle on whether there's a true "Derby effect"?
Because of examples such as Ryan Howard in 2006, Robinson Cano in 2011 and Prince Fielder in 2012. Each of these players actually had his slugging percentage rise after winning the Derby, in some cases tremendously: Howard slugged .582 during the first half of the 2006 season and .751 after the Derby.
Nine times the Derby winner has gone on to have a better slugging percentage during the second half of his season, including each of the last two winners, Cano and Fielder. Two other occasions produced a statistical draw: Andre Dawson in 1987 and Vladimir Guerrero in 2007 each saw his slugging percentage rise by a single point.
But that still leaves 18 times in which the Derby winner's power declined. Wally Joyner (1986) may be the most egregious case. He slugged .543 with 20 home runs in the first half. After the Derby, he dropped to a .335 slugging percentage with only two home runs.
For those who accept the theory that the Home Run Derby is a bad omen for a season's second half, it's generally held that players change their swing to more of an uppercut during the Derby and that mechanical change adversely affects them afterward.
But there are many reasons a player's slugging percentage could drop off. During the hot summer months, when teams can face grueling schedules, it's not unusual for a hitter's performance to suffer. Pitchers have had plenty of games to analyze opposing hitters and might find a flaw that wasn't apparent during the first half of the season.
Then, of course, there's pure, dumb luck.
Whatever it is, it isn't uniform, and a second-half decline isn't inevitable.
Which is good news for captains Cano and David Wright and their respective Derby squads. And better news for those players' teams.