Thunder Snow appears to be OK and has been looked at by the Track Vet. They are thinking he didn’t like the conditions of the muddy track. Possibly something he has never experienced before today.
I used to have a horse that didn’t like water. I’d be enjoying the scenery as she was galloping and suddenly we’d be flying through the air as if she was jumping a fence, all over a puddle about two feet in diameter, LOL.