I just started riding a new horse. He's green and young but has basically been a good boy everytime I ride him. The last time I rode him I did nothing different. But at a trot he decided he wanted to stop and pin his ears and swish his tail and not move forward no matter how much I asked. He's never done this. I'm so confused, I'm using all the same equipment. I got off checked his girth and then began touching his sides with the stirrups and he would get slightly annoyed with that. So I'm not sure if he's just being a bratty baby and testing to see what he can get away with or something is aggravating him. Any suggestions?