This redefines grand slam. Former tennis star James Blake was thrown to the ground and handcuffed outside his Manhattan hotel yesterday when police mistook him for a suspect involved in an identity theft ring. The 35-year-old told reporters that cops rushed him without warning. The ex-player — once ranked fourth in the world — said he believes his race was a factor but is more concerned by the amount of “blatantly unnecessary” force used. He was soon released, and Commissioner Bill Bratton has promised to investigate.