Question: What was the main topic of the United States Congressional hearing where Brian McNamee appeared to speak about this retired American baseball pitcher nicknamed "Rocket?"
Sentence (from "Brian McNamee"): Brian Gerard McNamee (born c. 1967) is a former New York City police officer, personal trainer, and strength and conditioning coach in Major League Baseball who is most notable for testifying against former New York Yankees pitcher Roger Clemens at a 2008 United States Congressional hearing that concerned the veracity of the 2007 George J. Mitchell Report.
Relevant evidence: Yes