Is there any possibility he was dinking around in the trailer on the way to the stable and pulled something?
Something being pulled or bruised may not have bothered him until the next day after standing around all night. And depending on whehttp://www.horseforum.com/media/graphics/misc/carrot.pngre/how, riding out forward and fairly straight on the track may not have bothered him.
It was a five minute trailer ride from our property to the stable and he's very quiet in the trailer (no kicking or anything) so I'm not sure. I'll feel his legs and see if there is any warmth or anything weird feeling.
I have free lunged him and done ground work with him since I've brought him home, and he's moving fine and willing at all gaits.