Serena Williams has pulled out of an exhibition at Madison Square Garden because of a left leg injury. Williams announced her withdrawal from the BNP Paribas Showdown for the Billie Jean King Cup on Thursday. She'll be replaced in the four-player field by former No. 1 Ana Ivanovic. The 12-time Grand Slam singles champion was to face Kim Clijsters on March 1 in what would have been their first... More...