My horse Rusty likes to jump most of the time. Sometimes, though, he gets lazy and then refuses to jump. He will run out at the last minute, sometimes even after his feet have left the ground (how I fell off last Thursday). My instructor thinks he's just playing games, and it's kind of frustrating. When he gets this way, he also won't respond to leg pressure and will refuse to move at times unless I use a crop on him. Also, when we turn corners, he has a tendency to bulge out. Any ideas on this?