0 (in tennis and some other games) two mistakes made one after the other by a player who is beginning a game by hitting the ball
I began the match at Wimbledon by serving a double fault, and lost several games by doing the same thing in the first set.
To fail to serve the ball over the net and in the proper place is called a "fault." The player has two chances and to fail in both is called "a double fault."
They are usually delivered as first serves, when the server does not risk a double fault.
She had double faulted as many as 19 times in a match and hit 50 mph first and second serves.
The shoulder injury not only resulted in her inconsistent first serves, but also her hitting high numbers of double faults.
Gonzalez coughed up two double faults in the first game of the third, including on break point.
Venus, though, gave her younger sister the break back, with three double faults in the one game.
Williams hit 37 unforced errors and 7 double faults in 2 sets.