I'm showing my youth here....
What's a lawn dart? And what's a "Lawn Dart" bounce?
A lawn dart is a large dart that one threw at a ring on the grass (hence the name, "lawn dart"). The safety nazis outlawed them because, if you were a real moron, you could kill yourself or someone else with the thing. The overall flight trajectory was sharply downward.
A "Lawn Dart bounce" is when the candidate comes out of the convention lower than when he started.
If you have never heard of lawn darts, thank Edwards and his cohorts
Lawn darts were a harmless little game that was around in the 70's. Kind of like Bocce Ball, only played with foot-long plastic darts tipped with a 4-inch steel spike. It was a heck of a lot of fun. I have no idea why the CPSC banned it...
A "Lawn Dart" bounce falls out of the sky and sticks...