Rusty Hardin, defense lawyer for Roger Clemens in the former baseball star’s perjury trial, attacked the credibility of the man expected to be the prosecution’s star witness during his opening arguments Wednesday.

The target: Brian McNamee, a former trainer who claims to have injected the former pitcher with performance-enhancing drugs.

“Brian McNamee is a liar,” Hardin said, adding that Clemens’ “only crime was having poor judgment of staying connected to” his former trainer over the years.

Hardin said that McNamee has changed his story over the years and only cooperated with federal investigators after being threatened with prosecution.

In his opening statement to jurors in Clemens’ perjury trial, Hardin reiterated that the former star pitcher never used performance-enhancing drugs and could trace his success to his intense work ethic and desire to succeed. Clemens is the most decorated pitcher in baseball history.

Hardin made a point of noting that Clemens continued to dominate Major League Baseball in the years after McNamee alleges he last injected Clemens with steroids in 2001.

Federal prosecutors have said that Clemens took steroids and HGH to extend his career and to help him recover from injuries as he got older.

“If he is taking steroids to prolong his career, why in the world would he stop and continue to play for six more years without a suggestion from any that he used steroids?” asked Hardin.

Hardin questioned the resources the government brought to bear on his client – noting that more than 100 law enforcement officers participated in the investigation.

The defense lawyer added that Clemens really didn’t have a choice about testifying before Congress. Lawmakers threatened to subpoena him if he didn’t appear to reiterate what he had been saying about not having taken performance-enhancing drugs in the days after former Sen. George Mitchell identified him as a steroid user in a lengthy report about performance-enhancing drugs in baseball.

In February 2008, Clemens testified before the House Committee on Oversight and Government Reform that he had never taken such substances. But McNamee, sitting at the same table as Clemens, testified that he had injected Clemens with steroids and HGH between 1998 and 2001.

The committee referred the matter to the Justice Department for a possible perjury prosecution, and Clemens was indicted last year on charges of perjury, obstruction of Congress and making false statements in his testimony.