What is a "ring sour" horse?

A ring sour horse is one that has become fed up with competition. This usually exhibits as disobedience in the ring or refusal to enter it (I did, however, once know a horse who would refuse to enter the ring and then be fine once inside...turned out he was fine if not asked to step over the rope being used as a gate, so I suppose he was afraid he'd trip on it).

Ring sourness is best cured by giving the horse some time off competing, going on a fun trail ride, or otherwise doing something other than competition. It generally means the horse is quite simply bored.