You know, it's so nice to be able to watch this again and again and again and see what COULD have been done, but even though the whole thing took 5 minutes, that seems like no time at all in a situation like that sometimes.
The announcer was quite calm and gave clear instructions. She saw the issue quickly and gave some warning. That was good. Perhaps in driving class, or any class for that matter, there should be (maybe there is already) a code word for runaway horse. You know, like CODE YELLOW!
However, who in their right mind would try to catch or STEP IN FRONT of a paniced horse??? DUH??? And where did the owner/driver go? This is the guy that should know best how the horse will react to certain things.
I think the best thing would be to clear the arena as soon as possible, which it appears they did do, even though it looks like it took forever. What other options do you have? Runaway horses happen at shows all the time. The big difference here is the cart and the additional danger it presents.
I don't show, I don't drive, so maybe my ideas aren't good, but that's all I've got.
Wow, that video was horrible. The guy whose horse spooked first should have brought his horse to the inside, rather than trying to stay on the rail. If he had done that, the whole thing probably never would have happened. Everybody else could have exited the arena while he got his horse under control.
And yea, you are supposed to step in front of a runaway horse. Of course, you don't try to do it when he's 10 feet away, but if all the people in the ring would have made a line to act as a wall to keep the horse running straight, one of them could have stood at the end and stopped it. I've seen it done before on a busy street with a runaway carriage horse. Trust me, as long as you give them time to stop, they will not run you over. Just stand in front of them, wave your arms, and tell them to "ho" or "whoa" or whatever.
Edit: Watch the guy at 3:35. He stood in front of the horse, and it didn't run him over. It turned and ran to the left. Imagine how easy it would have been to catch the horse if it couldn't have gone anywhere.