Woolums: The Home Run Derby myth

From SABR member Ken Woolums and Daniel R. Braunstein at FiveThirtyEight.com on July 14, 2014:

On Monday night, some of baseball’s best sluggers will compete in the Home Run Derby. One of them is likely to have a more disappointing second half of the season, and someone is then likely to blame the derby.

Case in point: At the MLB All-Star break in 2013, Chris Davis of the Baltimore Orioles had a stat line fit for a king. He had slugged 37 home runs, driven in 93 runs and had an enviable 1.109 OPS. Naturally, Davis was selected for the Home Run Derby, placing fourth. After the Derby, Davis’s season took a turn for the worse; he hit 16 home runs and battled with an injury on his hand — a blister he popped during the derby.

The decline in Davis’s power numbers fueled the belief that participating in the Home Run Derby alters a player’s swing in the second half of the season. We heard a similar story when Josh Hamilton’s HR production fell after the 2008 derby. And Bobby Abreu famously blamed the derby when he had fell back to Earth in the second half of the 2005 season.

But here’s the more likely culprit in these post-derby declines: regression to the mean. Data from the 2009 to 2013 seasons shows that although derby participants’ second-half stats do, on average, fall off, participants actually outperform the other top home-run hitters from the first half of the season.

Read the full article here: http://fivethirtyeight.com/datalab/the-home-run-derby-myth/

Originally published: July 16, 2014. Last Updated: July 16, 2014.