Compiled from wire reports In a damaging blow to the government’s federal perjury case against Roger Clemens, New York Yankees pitcher Andy Pettitte testified Wednesday that he was only 50 percent sure Clemens admitted to him that he had used human growth hormone. “As you sit here today, you believe in your heart of hearts and your mind that you very well might have misunderstood Mr. Clemens,” Michael Attanasio, one of Clemens’ lawyers, said to Pettitte. “Sitting here now, you’re 50-50 that you misunderstood him, is that fair?” Looking exasperated, Pettitte answered, “I’d say that’s fair.” That answer may end up haunting prosecutors, who have charged Clemens with perjury, making false statements and obstructing Congress for testifying at a House hearing in 2008 that he had never used performance-enhancing drugs. For those hearings, Pettitte had submitted a sworn affidavit saying Clemens had admitted to him in 1999 or 2000 that he had used growth hormone, a drug now banned by Major League Baseball. It was that testimony that set him up to be one of the government’s star witnesses against Clemens, his longtime mentor, teammate and friend.