Pittsburgh Steelers linebacker James Harrison wants the NFL to provide ''credible evidence'' before he agrees to an interview with league officials regarding a media report that linked him and other players to the use of performance-enhancing drugs. The NFL Players Association sent a letter on Harrison's behalf to NFL executive Adolpho Birch on Tuesday asking for more information. ''We have repeatedly requested that the NFL inform him and the NFLPA whether the NFL possesses any credible evidence (e.g., verified documents or verified testimony of witnesses) that warrants an interview of Mr. Harrison regarding a potential violation,'' union attorney Heather M. McPhee wrote. More...