Originally Posted by Gustavo Kuerten
What is the exact surface they're playing on, some kind of artificial clay?
It's typical american green clay Har-Tru http://hartru.com/har-tru-surfaces/green-clay
EDIT: Wikipedia: Green clay, Har-Tru or "American" clay, is similar to red clay, the differences being that it is crushed basalt rather than brick, making the surface slightly harder and faster. Green clay is packed to make the subsurface. It is then covered with a topping. These clay courts can be found in all 50 of the United States but are located primarily in the Eastern and Southern states...