NEW YORK -- Novak Djokovic, the odds-on favorite to win his 18th Grand Slam title at this US Open, is gone from the tournament in the most sensational default recorded in the Open era.
Djokovic, the top-ranked player in the world, was ejected from the tournament after he inadvertently hit a line judge in the throat with a ball smacked in anger while he trailed fourth-round opponent Pablo Carreno Busta 6-5 in the first set.
What exactly is a default, and are there other notable occasions when it has been used? Here are some frequently asked questions.