The Associated Press

Novak Djokovic knows it isn't model behavior when he loses his cool on the tennis court. Exactly two weeks after he was defaulted from the U.S. Open, and a day after he was warned by the chair umpire for breaking his racket in a fit of rage, Djokovic received an obscenity warning midway through a 7-5, 6-3 win over Casper Ruud in the Italian Open semifinals Sunday. The obscenity came in the third game of the second set, by which time Djokovic had a running dialogue with the chair umpire over a series of contested calls.