Over reach boots serve to protect the heels of the front hooves. Horses with long strides or young horses that are not yet properly balanced will easily kick their hind hooves against their front hooves. This can lead to serious injuries to the feet, especially if the horses are shod. Shod horses can also knock off the shoes of their front hooves in this way.
There is also an increased risk of such kicking when jumping or playing polo. The over reach boot is also often called a jumping bell boot, or bell boot. It is made of leather, synthetic leather, rubber or neoprene. The upper edge is often lined with synthetic fur or sheepskin to prevent chafing.