OK my 2 cents...I seriously doubt he was abused at a stable, but I would have him checked out, the trailer ride could have wrenched his back, but I really think it could be"Im not a very confident rider" at home you were relaxed, and no surprises...you move, you are a little excited just like he is, different surruoundings,people all that. It is an adjustment to be at a new place. The one thing about horses is YOU CANT LIE TO THEM!!! They can feel your energy before you get to the stall, now please do not misunderstand m I AM NOT calling you a liar, I'm just saying you may have walked up to him all"hi arrow how cool is this place" but in your head and your heart your in a new place trying to figure out the people and surrounding...you know all that. I have one that I can NOT hIDE ANYTHING from him NOTHING!! and he will act like a putz like that, he throws every single person that gets on him but me...why? he's big and black and from what everyone says is intimidating...I honest to god dont see it,but whatever! If I were you I would get trainer, then move him back,cuz you are NOT going to be able to show him if he is going to act like this away from home. Then you can make a more informed decision, but dont just give up on him...I promise you HE WOULD NEVER GIVE UP ON YOU! So think it threw, make alist of expectations, what are they realistically and go from there. Make Safety the first thing on your list, you cant do him any good if your hurt. Hope it helps.