I have the same problem with Pumpkin as you are describing - but not just x/c. We have had trainers check him over and ride him. He is just being rude. I do think though it is having to much energy, so whenever he continues with this behaviuor continously I let him off in the back paddock and run him until he listens to me no worries. Other wise, I will stay on, and spin him then make him stand, before moving off. I do this every time and he gets the message for the day. But like others have said, it is best to get a triner to help you.