Clay courts are unique in that the ball bounce leaves an impression in the ground, which can help determine whether a shot was in or out. Critics of red clay courts point to the constant need to wet them down, problems renewing the surface if it dries out, and the damage caused to clothing and footwear through stains. All clay courts, not just red clay, tend to cause a build-up of clay on the bottom of the shoes of the players, needing frequent removal.