I know that was a joke, and it was a good one that I enjoyed, but there are at least 2 I've heard/read of that were not injured (unless you count death as an injury).
I was looking for the various accidents for the other 10 which were all racing/training fractures and etc. except for the first of the 12
csb I grew up on a ranch and we had a stud that we actually bottle-fed as his mare died when she foaled but he was a high spirited mean dumbass anyway: When we penned cattle on our place we would erect a wing out of Powder River fence panels in the trap or small pasture next to the working pens to help funnel cattle into them, and the last panel was anchored with a few t-posts, so we left it out there semi-permanent. So picture a lone Powder River fence panel out in the middle of a 100 acre pasture, and our prize stud stuck his neck into it one day and then broke it and killed himself. Also had to euthanize my jr. rodeo calf horse after he just stepped wrong when I was practicing on him and that is pretty much why I quit that sport although I also got my driver's license around then also /csb
Panicky, fragile animals, some of it bred into them. I don't know why racehorse owners don't just buy race cars and blow those up instead. Probably cheaper.