When I was 9 years old, I got to watch something like that...
....from the front!
My brother (10 years old) and I wanted to use the garage to work on a go-cart we had built, but some inconsiderate person had parked a van there. Since dad was at the farm, and mom was gone to town (we lived out in the country in Monatana), we decided that we could push it out of the garage ourselves. My bro got up in the drivers seat to steer, and told me to get in front to push.
I pushed with all of my might, to no availe. This was a 70's Chevy van with a "3-on-the-tree" manual trans. My bro, reasoned that perhaps the trans was in gear and that he should take it out of gear to be able to roll it out of the garage. He fiddled with the shifter for a while with no luck. He then, wrongly, assumed that perhaps you would have to have the key in the on position to be able to shift out of gear.
Now here is the wierd part: This van had a clutch safety switch. It functioned perfectly up to that point, and it functioned perfectly from that point untill the van was sold some 10 years later. But for some ironic cosmic reason, it didn't work at that exact moment. So, with me grunting and straining, pushing on the front bumper, my bro turned the key on, and much to his surprise (much more to my surprise), the engine turned over, propelling the van through the back wall of the garage.
I remember the whole thing like it happened in slow motion. The van jumped at me once, knocking me down on my arse, then it jumped at me again hitting me at about neck hight with it's bumper, pinning me between two studs, then it jumped again, pushing me, and the wall back about 2-3 feet. By that time, my bro had finally realized what was transpiring and shut the key off.
The van loosened it's grip on my neck (I dont know exactly why it did it, maybe my bro had finally found neutral!), and I got to my feet. I was bleeding from the mouth. I wasn't in any pain, but I could tell that I had broken a tooth, because every time I inhaled, my lower jaw felt like it was instantly freezing. I started walking around in circles looking for my tooth. This must have freaked out my brother, seeing his bloodied, flattened bro making like a chicken picking.
As luck would have it, my mom had forgotten her purse when she left for Great Falls, and had turned around and come home. She got home about 15 miniutes after our little adventure. She saw me running up the driveway to meet her, my shirt front covered in blood, blood still trickling out of my mouth. She gave me the quick "mother's instinct" once over and decided that I needed to go to the hospital. Out in the wild in Montana, it is almost always faster to drive yourself to the hospital, than to wait around for the ambulance, so she ruled that she would drive me the 30 miles to the hospital...
...in the van that just ran me over!
[Edit]: I ended up having a (very) broken jaw and a broken collar-bone.