Even for the exceptional Novak Djokovic there must be no exceptions. A rule broken must bring a penalty and a lineswoman hit in tennis is worth disqualification. A man of mostly immaculate control with a racket must pay for his grievous loss of it.

Djokovic pulled a ball from his pocket at the US Open, half turned and flicked it in derision. Madness unfolded in the frustrated snap of a talented wrist. He was aiming for the back wall, or half-thinking of giving a ballboy catching practice, but instead hit a lineswoman in the throat. The game's finest player was inch-imperfect.