Novak Djokovic erred and has aptly paid the price for it. It's a bit harsh, some might feel, to be defaulted from a Grand Slam for unintentionally hitting the ball at a line judge. But the fact remains that Djokovic had no business swatting the ball away like that in the first place.

And it's not the first time in that US Open fourth-round match against Pablo Carreno Busta that he has done so. Just that this time it struck an official on the throat.