In the English style of riding, sometimes you may notice a rider wearing extra material around their calves. These are known as half chaps (I've included a picture below for better reference). Riders may choose to wear half chaps as a way get a better "feel" of the horse and keep your leg in the proper position. The coefficient of friction is increased by riding with half chaps as most have a grippy (for lack of a better term) fabric on at least the inside of your calf. The coefficient of friction is much greater using chaps than it would be wearing jeans, breeches or any other pant. When riding the goal is to keep your shoulders, hip and heel all in a straight line from top to bottom. Half chaps aid in lessening the movement in your calves as you ride, which allows you to keep the straight line from shoulders to heel.