Printer-friendly

June 22, 2006

Schrodinger's Bat

More Humidity

by Dan Fox

"The number one reason, for me, is the calming effect of the humidor. That's made it a more realistic game for pitchers. And not just our numbers–opposing numbers are down, too. It's created an environment that keeps the balls from shrinking."-Rockies manager Clint Hurdle

Two weeks ago I offered a few theories on why run scoring at Coors Field is down this year in response to a rash of articles on the "humidor effect" last month. Through games of June 15, some back of the envelope calculations show that run scoring is about 5% higher at Coors while home runs are up about 16%, whereas historically those numbers would be around the 25% and 50% range respectively. Obviously small sample-size caveats apply, but in that article we found that through the first two months of the season, run scoring and home runs have never been this low in Coors, a fact that verified Hurdle's statements and justified all the talk around the league.

Among the theories offered in that column were that a better pitching staff and weaker hitting have the effect of dampening park effects (in other words, the effects are still there, but the team’s makeup conceals them), soggier baseballs (made so by leaving them in the humidor longer) make it harder to take full advantage of the environment, and that longer grass has some effect on batted balls. This week we'll explore the last two of these theories in a little more detail, with the help of some additional data. So, as Will Carroll says, powered by my recent trip to Fenway Park, let's go.

Soggier Baseballs

As mentioned in the previous column, it has been reported that the Rockies are now simply using balls that have been in the humidor longer. The effect of that practice is ostensibly to have the baseballs absorb more moisture, making them heavier with a lower coefficient of restitution (COR).

COR is a measure of the "bounciness" of the ball, or more precisely, it’s the ratio of the velocity of the ball when rebounding from a hard surface with its initial velocity. Major League Baseball specifies that the COR must be between .514 and .578, as measured by firing balls at 85 feet per second at a wall of ash.