The former strength coach for Roger Clemens testified Monday that he supplied other big league ballplayers with performance-enhancing drugs and shared that information with law enforcement officials.

Brian McNamee, former major league baseball pitcher Roger Clemens' former strength coach, leaves after testifying in the perjury and obstruction trial of Clemens on May 14, 2012 in Washington, D.C. (Brendan Hoffman/Getty Images)

Brian McNamee’s admission for the first time to jurors in the star pitcher’s perjury trial was intended to suggest that he was not out to get Clemens when he began confiding in federal agents in 2007.

Defense attorneys for Clemens had vigorously opposed allowing McNamee to testify about the other ballplayers because of concerns about “guilt by association.” But U.S. District Judge Reggie Walton ruled Monday that the government could introduce the information as a way to bolster McNamee’s credibility.

For days last week, McNamee endured aggressive questioning by Rusty Hardin, Clemens’s lead attorney. He was forced to acknowledge under cross-examination that his story about injecting the baseball legend had evolved over time and that he had lied to federal agents, and separately to police in a criminal investigation in Florida.

But McNamee largely remained calm and unapologetic last week about his changing story. He testified, for instance, that he initially minimized to federal agents the number of times he allegedly injected Clemens to try to reduce the potential harm to the pitcher.

McNamee is the only witness with firsthand knowledge of Clemens’s alleged use of performance-enhancing drugs. Clemens is charged with perjury, obstruction of Congress and making false statements for lying to lawmakers when he denied using the banned substances during House hearings in 2008.

Testifying for a sixth day and final day, McNamee said he was loyal to Clemens and had no incentive to damage his employer’s reputation by talking to federal agents. McNamee agreed to cooperate, he said, to try to avoid getting in trouble for distributing the banned substances. He told authorities about his involvement with several players, including pitcher Mike Stanton, infielder Chuck Knoblauch, and Andy Pettitte, who earlier gave conflicting testimony about his memory of a conversation with Clemens about a human growth hormone.

Before leaving the stand, McNamee said he regretted helping Clemens and others with performance-enhancing drugs. As a result of the federal investigation, McNamee said he became unemployable, destroyed his marriage and his relationship with his children.

“I shouldn’t have gotten involved; I should have just educated and left it at that. I shouldn’t have enabled,” he said.

The trial, now in its sixth week, continues Monday afternoon. Prosecutors are questioning a young neighbor of another ballplayer Jose Canseco, who attended a pool party at Canseco’s home in 1998. McNamee alleges that Clemens and Canseco talked about performance-enhancing drugs at the party, but defense lawyers say the star pitcher was playing golf that day.