Wow. That is awful. 3-day Eventing has become very dangerous. The jumps are too big and difficult for horses and riders to clear. It is becoming a growing problem in this sport. It is very depressing to hear when people and horses die doing it.
when i was a junior rider, back in the 1960's, we lost a hunter rider, 12 yr old blythe davis of bloomfield hills, MI., on course. riding is dangerous, in general, not just eventing. her horse fell on her. a human cannot sustain a 1000 weight crushing their chest.