PB…
I hear the cement mixer running. So, I believe that the thick plastic guard between the motor and the drum broke loose and caught the motor teeth just right to give it tremendous counterclockwise velocity.
Thereby, making this plastic guard with a chunk missing off it, most likely, fly backwards toward and into the house.
When this thing hit the guy in the house, the jagged edges cut him, ergo, the 24 stitches. When the guy gets hit, his immediate reaction is to jump back and then he falls out the door.
That's what anon is seeing.
Wow! What a freak accident!