Okay, I'll do the math.
It's theoretically possible to cut through a board in a tenth of a second by throwing a spinning saw blade at it. Here's how you can compute the minimum rotation speed required: count the number of times the blade spins while cutting through the wood when shoving a circular saw through as fast as possible without stalling. You get abut five seconds, or 500 blade rotations. Any fewer and the blade chokes on too much wood per cutting tooth. So on average, the blade needs to be spnning at 300,000 RPM. As the blade cuts the wood, it loses rotation energy. The 300,000 is the mean rotation speed from an unknown high to nearly zero as it exits the wood. In other words, he's gotta get it spinning on the order of a million Hz as it leaves his arm. I think his gloved hand is more cuttable than that board. But if the guy gets it going too fast, the blade will bury itself into the soft earth afterward. He's gotta get just enough spin to cut the wood, and no more.
It's also true the blade would not bounce upward. Unless... The blade hit the wood and just bounced off.
