I find that if I loc the chain brake and use that sawing motion... I don't need my ear protection and I don't use so much gaaaaaaaaaaas...
Scary thing is, most folks don't even think about the root ball standing the tree back up. I've seen them stand up twice that fast . And yes the sawing motion is a classic!
Wish you could meet an old friend of ours. We don't see them any more but I always think of him when cutting anything. Yes, with the chain saw, he is never still. But give him a skill saw and he can't hold the saw down there either! Yes, all the way across a 4 x 8 sheet he is going up and down with the skill saw. Jig saw, same thing. Amazing. Also the guy in the picture perhaps could use a few tips on sharpening a saw and on proper method of standing while cutting.
I've had that happen to me a couple times...scared the chit out of me the first time, but ever since then I try to cut as close to the root ball as I can, and prop the trunk with rounds so it won't roll when the root ball moves back in the hole.