The story I heard...
...was that the announcer kept saying "do you want to see Obama run down by a bull?" And that the clown was inciting the crowd to scream for that to happen. And that the crowd did scream for that to happen. From what I heard, it was a pretty sick event.
However, I don't have more than one eye-witness account to go on, and I do not know that person personally. You would have to ask the Governor of Missouri to explain why he took the stand that he did.