Ah, the paparazzi.
I think the horse may have mistaken them for zombies.
Madonna falls from horse in Hamptons after paparazzi spook animal
"Madonna was tossed to the ground Saturday when her horse was startled by photographers while riding on a Hamptons estate. The Material Mom was rushed to Southampton Hospital with minor injuries and bruises after a fall while riding at the Bridgehampton farm of celebrity photographer Steven Klein."