I purchased an OTTB in December. He's a 6 year old, 16.3 hh gelding, who's been off the track for a year and had a pretty successful career. I haven't worked him much, but the last month he has developed a habit of stopping and refusing to move under saddle. Once I get him going, he'll happily trot and canter with little leg and moves forward or slows appropriately. He's unresponsive to kicking or a crop until he's "ready" to move. This also includes lunging either on a line or in a round pen. He will outright refuse to move, even with lunge whip included. I get after him heavily, but I worry that my efforts are just further proving he's in charge as no amount of coercion is effective. He goes in a rubber snaffle and an english saddle, all of which fit him. Occasionally he pulls the same act when leading, but on the ground I can get him going quicker. If this offers any additional suggestions, he does have a rehabbed drop hip and a small sesamoid fracture (which he apparently raced on after it healed).