A common stable vice
The unnatural conditions in which the domesticated horse is kept today, can lead to a variety of abnormal behaviour patterns called ‘stereotypies’ or ‘vices’.
Weaving, wind-sucking, crib-biting and box walking are just some of the habits that horses may acquire because of the restrictions placed on them by domesticated life. Generally speaking these behaviours are not especially harmful to the horse, but once acquired they can be very difficult to break. Often it is considered more stressful to try and break the vice once it is established, than just to leave the horse to perform the behaviour. The bigger issue is of course that the behaviour is a sign that the horse is unhappy in his environment, and that in certain examples like wind-sucking their can be health consequences.

Box-walking
Horses who continuously walk around and round their stable are known as box-walkers. Research to date has suggested that sometimes this habit is inherited, but generally speaking, the major contributing factor is confinement in a stable in the first place. The method of weaning used when the horse is a foal is also considered to be important in the development of this behaviour.
Usually it is easy to spot a box-walker simply by looking into the stable. Even if he is not moving at that particular moment, you will see the track in his bedding formed from the continuous repetitive movement. If you are looking to buy a horse make sure you see him in the stable, so that you can see if he has this vice. However, it is also worth noting that certain horses only box-walk at specific times, like when they are left-alone or when they are anticipating being fed.

Horses who are stabled for long periods of the day may box-walk to the extent where the muscles on one side of their body develop more than those on the opposite side of the body, as the box-walking normally occurs in one preferred direction. Some horses will box-walk to the extent that they are exhausted by the effort, and thus unable to work at the level required of them.
Some people try and prevent box-walking by placing obstacles in the stable, like bales of hay or tyres. However, this is only likely to increase the horse’s level of frustration – not improve the situation. The kindest thing that you can do for a box-walker is to ensure that the horse has plenty of exercise to help satisfy his need to be on the move and to turn him out as much as possible, in the company of one or more calm companions. Sometimes a complete change of environment can solve the problem – for instance moving your horse into a more sociable barn environment may be of benefit. Some horses that box-walk at one particular stable yard, entirely stop the habit at another.

Whether or not you choose to buy a horse you know to be a box-walker depends on what you want to do with him, and how you plan on keeping him. If he can be in the paddock for long periods each day, it may not be an issue. If you plan to stable him but keep him fit with regular exercise, you may find this is sufficient for the horse or you may find it difficult to maintain his condition with this regime. Unfortunately it is impossible to tell!
REMEMBER: The best and kindest approach to stable vices is to tackle the underlying cause, not the symptoms.