Adam Dunn is on a historically bad pace this season, and it appears that part of the reason is that he somehow lost a chunk of bat speed while making the offseason journey to Chicago. Take a look at the data chart, which shows the average speed the ball came off of his bat and the average true distance the ball travelled on his home runs this year and the previous five seasons (from ESPN Home Run Tracker).
What’s eye-catching is that the ball is coming off of Dunn’s bat 2 mph slower than any of the previous five seasons, and 5.2 mph slower than his best bat-speed-average in 2008. This change appears to have a significant affect on how far the ball travels. This year his average home run is travelling 393 ft. In previous years he’s never averaged below 410 ft. The 2 mph change appears to have dropped the distance the ball travels off his bat by more than 15 feet! (Physics research backs this up: In terms of turning a hit into a homer – Against a 94-mph fastball, every 1-mph increase in swing speed extends distance about 8 ft (Popular Mechanics))
And now if you take that 15 feet and apply it to Dunn’s hit chart below, you can easily see the difference it would make if he could get that distance back. It appears that there are easily six fly ball outs that would’ve gone for home runs with an extra 15 feet, and that’s just at Dunn’s home park (U.S. Cellular Field). Assuming the same on the road, that could be a total of 12 additional home runs. That’s a considerable number. Even with 12 more home runs, Dunn would still be hitting under .200, but at least it would be a little more tolerable for Sox fans if he had 21 home runs right now instead of nine. For the sake of his career, Dunn needs to find a way to get his bat speed back.