The worst feature of clay courts is the contrast in speed between the slow clay and the extremely fast lines, which are made of plastic or coated fabric. This introduces a significant extra element of luck into the game; balls that hit lines are often nearly unplayable. One might argue that it isn't luck if you aim for the lines, but aiming for lines is generally much too risky to be a wise tactic; it shouldn't be rewarded.
Hitting a ball that skids off a line can send an unpleasant jolt to the arm, and the accumulation of torsional forces from off-center hits caused by unpredictable bounces off the uneven clay surface itself may contribute to arm injuries such as tennis elbow.
Clay is also slippery, and slipping can cause leg strains and injuries. Changing direction on a slippery surface is more difficult, so true clay-court experts learn to slide into the ball so that they will have stopped by the time they need to change direction, but the sliding itself sometimes causes injuries, as players can hit slow spots or simply have a shoe angled incorrectly.
No court surface varies in the height of the ball's bounce as much as clay. On cold, wet clay, the ball bounces quite low; on dry, hot clay, it bounces quite high. The outcome of a tournament can thus depend more on weather than it would on any other court surface, another increase in the potential influence of luck.
Unless a clay court has an advanced and expensive drainage system, any substantial rain will make the court unusable for at least several hours, often a full day.
Clay must be watered and groomed regularly, usually at least daily. Like all earth, clay courts are subject to erosion by wind and rain; new clay must be brought in to replace the losses. Some of the lost clay can also be found on the players, as it goes home on clothing and in shoes. Frequent clay-court players usually have the beginnings of a court inside their houses after a while. The worst place for clay dust to end up is in the player's eyes; as you serve, you knock a small cloud of clay out of the ball's fuzz, and it rains down on your head.
If you're a sidespin artist, clay will blunt one of your favorite weapons. The loose surface dissipates sidespin so that heavy slice serves and sidespin-slice backhands, for example, turn less dramatically than they do on other surfaces.
