NEW YORK Top-seeded Novak Djokovic was defaulted from his fourth-round match at the U.S. Open after he accidentally hit a line judge with a tennis ball Sunday. Djokovic had just lost a game to his opponent, Pablo Carreno Busta, to fall behind 6-5 in the first set. As he walked to the sideline for the changeover, Djokovic smacked a ball behind him. The ball hit a female line judge, who dropped to her knees at the back of the court. After a discussion of several minutes with officials on court, Djokovic walked over to shake hands with Carreno Busta, and the default was announced.