FILE - Spain's Rafael Nadal runs and slides to return a shot in his second round match of the French Open tennis tournament against Argentina's Facundo Bagnis at the Roland Garros stadium in Paris, France, Thursday, May 26, 2016. The French Open is the only Grand Slam tournament held on clay — which actually isn’t truly clay, but the dust from red brick on top of a layer of crushed white limestone. (AP Photo/Alastair Grant, File)