So, I just checked to see what the proposed reason behind Big Brown’s loss were…
Some people are blaming the quarter crack in his hoof, others are very wrongly blaming the jockey, some say it was the lack of his steroid booster…  since no one can agree and none of the reasons seem to have much basis other than personal opinion, that frees me up to give an opinion of my own…
The bump at the beginning wasn’t to blame for the whole problem.  But it may have been part of the whole.  Brown was also being held back much longer than usual (and I’m not pointing fingers… it made perfect sense) because it was a longer race.  My personal opinion is that he could probably have done it without being held quite as long, but it’s always better to go with a sure… “he can blow them away for this long, but I don’t know about that distance” than “I think maybe he can do it anyway”.  He got pulled to the outside when there wasn’t an opening…  If my memory serves, everytime he got going, he was bumped, shut down, slowed down, or pulled out.  Not due to anyone’s incompetence, simply because that’s the way a race runs!
When Kent tells him it’s time, he just hangs back.  My invalidated, unasked for, unproveable opinion is that the horse had been shut down so many times on the track already, that he just settled in for an exercise run.  If you watched the post race shots, he was strutting.  He was posing.  He didn’t think anything of being pulled up early.  He certainly didn’t appear lame.  He didn’t seem tired.  He just decided that if he wasn’t SUPPOSED to go, he wouldn’t. 
There you have it.  For what it’s worth. 
Sad, though.  I hope they give him a chance to redeem himself, because he’s got a lot of go.