One of the women I work with almost had the same thing happen to her. She got very lucky. She was digging post holes and she got off the tractor with it running and grabbed the bar to help put downward leverage on the post hole digger. Her shirt got caught in the drive shaft and started pulling her into it. Just as she got up to the drive shaft the shirt ripped apart and the driveshaft pulled it off of her. I have dug several post holes with my tractor and not once have I ever felt the need to get off of my tractor to assist the digger. If I cant get through the spot I am in. I shut the tractor off and pour water in the hole then wait a while and try again. If that dont work I move the tractor to a spot a bit further down and try again.
Wow, thats a major point to all who use a tractor. Don't get off it without thinking about your actions. As I was brush hogging a few weeks ago, i was often off away from others in the forest. If something suspicious came from the hog, I would raise the unit, turn off the PTO, set the brake, maybe kill the engine if I thought I'd need to do something; other than that a visual inspection I'd idle it down. My arms, My life are not worth the risk.