So I like to take my horse, Stanley, out to ride in the hay field where I sometimes turn him out. However, since sometime last autumn, he has been bucking and hopping, sometimes almost throwing me off, when I ask him for a trot or canter. He will often comply for a bit before starting to buck. I try to keep driving him forward with my leg but he ignores it. I tried using a crop once but it made things worse. There have been no changes to his tack or anything and I have worked very hard to keep my seat, hands, etc. relaxed. What do yall think this could be? Maybe he's barn sour or having separation anxiety since his friends are over in the paddock. But it's strange because he hasn't always done this. Any thoughts? Thanks!