Things I learned watching tennis:
The S's Rule:
Novak Djokovic-Serbia
Rafael Nadal-Spain
Roger Federer-Switzerland
Andy Murray-Scotland (although Murray hasn't been playing for over a year now)
Some names occur quite frequently:
John (McEnroe, Isner)
Juan (Juan Carlos Ferrero, Juan Martin del Potro, Juan Ignacio Chela, Juan Monaco)
Ivan (Lendl, Ljubicic)
Nicolas (Almagro, Mahut, Devilder)
Andy (Roddick, Murray)
Denis (Istomin, Kudla, Shapovalov)
David (Ferrer, Nalbandian)
Sam (Querrey, Groth)
Roger and Rafael seem to be unique! Novak is unique in having that name as a first name, rather than a surname.