People like to see stuff get wrecked. Which is why demolition derbies are popular attractions at county fairs. A county fair in the Midwest is offering a new twist on this staple of Americana. Instead of a demo derby featuring old cars, one county fair in Minnesota is sponsoring a smash-up derby featuring riding lawn mowers. Here's my story, which aired on NPR's Only a Game , on a lawnmower demo derby.