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 "Roger Clemens"): Clemens was one of the most dominant pitchers in major league history, tallying 354 wins, a 3.12 earned run average (ERA), and 4,672 strikeouts, the third-most all time.
Relevant evidence: No