Horse will run away while on the field: A horses natural reaction to pain is to run as when a predator is present.
Horse is unwilling to stop: A horse needs to curl her back up (flex the dorsal muscles) to allow the hind legs to go under to stop.
Chronic back pain will discourage the horse to use her back this way thus making her unwilling to stop. If the horse feels pain when asked to stop they will feel punished every time they try to slow down or stop.
Horse will run flat footed with a flat back under saddle: This way of galloping makes the horses maneuverability on the field difficult.
COMMON SIGNS OF ILL-FITTING SADDLE FOR THE RIDER:
Rider feels "left behind" causing them to have to "climb" out of the seat to prepare for the swing: This is a common problem and can adversely effect the timing of the riders swing.
Rider is pushed forward in the seat with their legs too far back: This too can negatively effect both the riders balance in the saddle and the timing of their swing.
Riders knees hang over the front of the saddle: This position makes planting the thigh or knees on the saddle very difficult and unstable and will surely cause the rider to be off balance.