A horse has fallen down on the green grass and the jockey riding on top is trying his hardest to not fall off.
The jockey is trying not to fall off the horse.
The jockey trying not to fall off the horse as the horse fallen.
The "jockey is trying not to fall off the horse" is a rephrase of "jockey riding on top is trying his hardest to not fall off."
Jockey is trying his best to not fall