WASHINGTON -- Roger Clemens' defense team had its first opportunity to cross-examine a witness for the prosecution in open court Monday, and it proved to be a contentious session that included numerous objections by the government as well as the possibility that the door has been opened for more baseball players to be mentioned during the trial.

Direct examination by the government of Congressional staffer Phil Barnett concluded just before a lunch break in Judge Reggie Walton's courtroom at the U.S. District Court for the District of Columbia, where Clemens is being tried on federal charges that he lied under oath to Congress.

Defense attorney Rusty Hardin conducted his cross-examination of Barnett through the afternoon of the seventh day of proceedings in the case, using his questions to suggest that the 2008 Congressional hearing involving his client was a "show trial," while beginning to attempt to chip away at the charges against the former star pitcher.

By the end of the day's session, Hardin was breaking down the 15-point charge of obstruction of Congress -- only one of which must be proven by the government to attain a conviction -- by addressing each statement in which the government charges Clemens lied, questioning Barnett as to "what possible legislative purpose" each particular question could have served.

Barnett's repeated answer, and the main thrust of his direct testimony, was that Clemens was invited -- a characterization Hardin disputes -- to testify before Congress to determine the accuracy and reliability of the Mitchell Report on performance-enhancing drugs in baseball, which included the contention that Clemens used steroids and human growth hormone supplied by strength and conditioning trainer Brian McNamee.

Clemens, who won a record seven Cy Young Awards in his 24-year Major League career, is charged with one count of obstruction of Congress, three counts of making a false statement and two counts of perjury stemming from his Feb. 5, 2008, deposition that involved questioning from Barnett and his Feb. 13, 2008, appearance before the House Committee on Oversight and Government Reform, during which he denied ever using performance-enhancing drugs.

In his cross-examination of Barnett, Hardin attacked the notion that Clemens was testifying voluntarily, because several players in 2005 Congressional hearings were subpoenaed to testify, and he suggested that likely would have been the case if Clemens refused to undergo a deposition and testify in an open hearing. He also pressed Barnett on whether the deposition would have been enough to indict Clemens, revealing that defense counsel had suggested in lieu of holding a hearing a public event with Clemens and committee members to send a message to children about staying away from performance-enhancing drugs.

"[The hearing] was solely to get Roger Clemens, because he dared to challenge them," Hardin said outside the presence of the jury as the two sides argued over the validity of the line of questioning.

As Hardin explored what legislative purpose Congress had in deposing Clemens and holding the hearing by going through statement by statement in the obstruction charge, lawyers for the prosecution and another for the House of Representatives, the latter there in support of Barnett in his testimony in the trial, objected several times.

The government ultimately argued that Hardin had opened the door to mention of other players and how their use of performance-enhancing drugs had been mentioned in the Mitchell Report, with the names of Mike Stanton, Chuck Knoblauch, C.J. Nitkowski among those possibly coming into play now. Walton seemed to indicate that if the defense does pick at each question, the government could introduce the other athletes and other possible witnesses as corroboration of the Mitchell Report findings.

"Obviously, Congress is going to look at the entire mosaic, and that one question is part of the mosaic," Walton said initially, reinforcing that thought after checking case law.

Behind the scenes, the defense issued a response to the government's motion on just how much of strength trainer Brian McNamee's "prior bad acts" will be allowed in the trial.

On Monday morning, the defense submitted a response to the government's assertion submitted Friday that the jury should not hear about many of McNamee's actions as a New York police officer and then as a strength trainer, including details of his alleged sexual assault of a woman in a Florida hotel pool in 2001. The defense submitted documents that accused McNamee of other bad deeds, including loan fraud, participating in a prescription-drug ring and driving under the influence.

Whereas the government contends that McNamee's "prior bad acts" are not relevant to his truthfulness in this case, the defense asked Walton to either deny the government's motion to keep the information out of the trial or reserve ruling on the scope of the defense's cross-examination of McNamee at this time.

"As the government acknowledges through the lengths it is taking to secretly protect him, Mr. McNamee is a serial liar who has engaged in myriad episodes of relevant misconduct," the defense response read.

Once Barnett's cross-examination is complete, the government will call its next witness -- but it has objected to disclosing who that witness might be. Along with McNamee, Yankees pitcher Andy Pettitte is expected to testify for the prosecution about the deposition he gave Congress in 2008 that recounted a conversation he had with Clemens before the 2000 season in which Pettitte claims Clemens admitted using human growth hormone.

This is a retrial of the case after the first attempt to try Clemens ended in a mistrial last July, because the prosecution allowed the jury to see inadmissible evidence, namely the affidavit Pettitte's wife, Laura, gave supporting her husband's recollection. That affidavit is among the evidence that might now be allowed in the trial if the government succeeds in convincing Walton that the defense has opened the door to it.