Roger Federer, of Switzerland, returns to Leonardo Mayer, of Argentina, during the first round of the U.S. Open tennis tournament, Tuesday, Sept. 1, 2015, in New York. (AP Photo/Matt Rourke) (Matt ...

It’s always been the case that no playing surface more than clay reveals the raw physicality of world-class tennis. And seemingly every five years, an athletic upgrade arrives. These days, the ...