Good God...it makes no sense? Lemme 'splain it: the rear tires hitting are gonna drive the car forward pretty much instantly; certainly close enough in time to determine leaving early during what's supposed to be "a street race at the track" in their words.
My point is that the tree might be confusing things a bit in the sense that it introduces .001 reaction arguments, where the flashlight deal that apparently most of those guys are used to comes down to video of the rear tires to determine when the driver launched the car.