Hey, accidents happen. I knew a horse that when his owner tried to catch him he ran around his paddock. He was just running around, they weren't pressuring him, and he ran into one of the posts and impaled his chest on the bolt for the gate. Luckily, my mom was there and with quick thinking, stuck her hand in the horses chest to stop the bleeding. The vet was called out, the horse was stitched up, and he healed just fine.
Horses are impossible to predict all of the time and there is no reason to be criticizing the OP when we've only seen 26 seconds of a poor quality video.
To the OP, I hope you all the best in your horses recovery!
"You know, for as long as I can remember, I've had memories." ~Colin Mochrie