Serena Williams has decided to pull out of the US Open because of a torn hamstring, she announced on social media Wednesday.Williams, who has won the event six times in her career, said in an Instagram post she was advised to let her body fully recover over playing in the Grand Slam tournament in Queens, New York.«After careful consideration and following the advice of my doctors and medical team, I have decided to withdraw from the US Open to allow my body to heal completely from a torn