What makes a hard court fast is its relatively smooth and firm surface. When the ball strikes a smooth surface, it encounters less friction to slow it down and fewer and smaller vertical protrusions to push it upward. The smoothness of a hard court increses as the quantity and grain size of the sand that is mixed in with the paint topcoat decreases. Fast hard courts are generally too firm to allow the ball to depress the surface and be slowed as a result.
A faster court gives each player less time to react to the ball, and this makes it easier to hit winners. Easier winners can encourage impatience, a common vice in tennis players, and discourage the virtue of learning to think beyond the current shot. As sheer power becomes more effective, placement gets less emphasis. With shorter points on average and fewer angle shots to chase, players tend to get less exercise per match on a fast hard court.
The body enjoys less exercise as a whole on a fast hard court, and the arm endures more stress from the greater incoming speed of the ball and a greater likelihood of an off-center impact due to insufficient time to line the racquet up properly. The cumulative impacts of running on hard courts are also tough on leg joints, although the legs are spared the strains caused by slipping on clay and grass. Cushioned hard courts ease routine impact strains on the legs, but in extreme heat, some rubberized surfaces can cause injuries when they become sticky enough to grab onto a shoe more than the player expects.
