The jockey you see getting smoked by a fence in the GIF above is named Lewis Ferguson (don't worry, he's not dead), and this happened during what was apparently his first-ever race with fences. Poor Lewis made some mistakes.
If you watch the video clip above, it sure looks like Ferguson leapt from his horse's saddle on his own accord. This leads me to believe that, he decided fence races weren't really his thing, and thought it would be a good idea to just bail before the next jump.
"I'VE MADE A MISTAKE!" he probably thought after the first jump.
And then, while somersaulting through the air, "I'VE MADE AN EVEN BIGGER MISTAKE!"