Kirsten Flipkens dropped her racket, put her hands on her hips and stared. Agnieszka Radwanska had done it again.

It was in Miami last year, and Radwanska was out of position at the net. She sprinted to her right and put out her racket for a rocket Flipkens backhand that never came, because the ball hit the net and bounced straight up. Radwanska overran the ball. She did a pirouette. She started to swing again before she could see the ball. She made contact as she completed her 360. The ball fell into the open court for a...