You would think that people would know not to stand too close to cars that have purposely lost a measure of control in order to have fun. You would think that people would know that these cars, especially when not driven by professionals, can be unpredictable. This man did not know.
Let me break this one down, step by step.
1) BMW goes drifting, in a circle. Woo.
2) BMW continues to go slippy-sideways, in a circle. Woo.
3) Spectator decides he wants to really spectate, and proceeds to get ridiculously close to the edge of the asphalt in which the BMW is going slippy-sideways, so that he can cheer the occupants of the BMW on. Woo.
4) The BMW, which previously had been experiencing a condition known as "controlled oversteer," begins to experience a condition known as "uncontrolled understeer." The driver, seeing that he was heading straight into a group of spectators, especially our hero who wants to really spectate, decides the best thing to do is not something silly, like hitting the brakes. No, that would be far too safe, and would end all the "Woo"-ness a bit early. Instead, he decides to gas it, returning the car to its previous condition of controlled oversteer.
5) This whips the tail around, just enough to just completely WRECK our hero. Our hero lies on the ground, probably not dead, but also probably not not injured. I don't really know, because A) the video description doesn't provide any additional information and B) the video appears to take place in Poland, and despite a portion of my ancestors hailing from the city of Bialystok roughly 100-and-some-odd years ago, I don't speak a word of Polish. So let's just assume he's injured, and now has a good story for his life.
6) The driver of the BMW, sensing that the nice little "SMACK" followed by a dull "THUD" was probably not a good noise, comes to a halt with grace and style, right in front of the man whose day he just ruined. Nice.
This is why you don't stand too close to drifters.