Signs of poor saddle fit can help you identify when you need to adjust or perhaps even change your saddle. Saddles are intended to distribute the weight of the rider over the back of the horse in the way most beneficial to the horse and the rider. Poor saddle fit can disrupt this, causing an uncomfortable ride and possibly even injuring your horse.
Poor saddle fit can mean the saddle is either too wide or too narrow, not properly padded, or just plain wrong for the job you are doing. If either you or your horse has gained or lost a considerable amount since your saddle was fitted, there is a chance it is no longer a good fit.
One sign of poor saddle fit is friction rubs or white hairs in the saddle area. These are caused by uneven weight distribution rubbing on pressure points on the horse’s back. Over time, these will develop into white hairs or friction rubs.
Rocking from side to side or rolling to one side can be a sign of poor saddle fit. Before blaming the saddle for this, however, take a close look at the rider. If the rider is not properly balanced in the saddle, this rolling or rocking can result. If the rider 
is well-balanced, though, take a look at the saddle fit.
Another sign of poor saddle fit is dry spots following a long ride. When you take the saddle and pad off after a long ride, you should see an even amount of wetness along all the contact points. Spots that are dry can indicate pressure points.
Tipping up in the back is a clear sign of poor saddle fit. In most cases, this is due to the tree (or foundation of the saddle) not being properly fitted.
Sores under the saddle, temporary swelling after the saddle has been removed, and scars under the saddle area are also signs of poor saddle fit. Not all signs are physical, though. Some horses will exhibit behavioral problems when faced with a poorly fitting saddle. Resistance to be saddled, pinning ears, and objections to being saddled can all be behavioral signs of poor saddle fit.
