Three-time U.S. Open champion Kim Clijsters has been ... "And I think it’s kind of Federer's way of interacting with the ball kids, letting us know that he knows the job we’re doing.

Over the course of the Open era, and especially in the last 15 years, it has been tacitly decided that it’s the job of the ball kids to do the players’ bidding. The most obvious—and gross ...