WASHINGTON -- One minute Roger Clemens was on trial for his freedom. Then, on just the second day of testimony, it was suddenly all over and the former baseball star was outside signing autographs for fans.

Almost as soon as it began, Clemens' perjury trial ended Thursday -- in a mistrial the judge blamed on prosecutors and said a "first-year law student" would have known to avoid.

U.S. District Judge Reggie Walton called a halt to the trial under way after prosecutors showed jurors evidence that he had ruled out -- videotaped revelations that a teammate had said he'd told his wife Clemens confessed to using a drug.

Walton scheduled a Sept. 2 hearing to determine whether to hold a new trial. Rusty Hardin, Clemens' attorney, told reporters, "I wouldn't even hazard a guess" about what Walton will decide. Hardin said he needs until July 29 to file the motion for the hearing. The prosecution has until Aug. 2 to respond.

Walton told jurors he was sorry to have wasted their time and spent so much taxpayer money, only to call off the case.

Walton scolded prosecutors and said he couldn't let the former All-Star pitcher face prison if convicted on such "extremely prejudicial" evidence.

"Mr. Clemens has to get a fair trial," Walton said. "In my view, he can't get it now."

Hardin, who had asked for the mistrial declaration, patted an unsmiling Clemens on the back as the judge announced his decision. As he left the courthouse, Clemens did not comment but accepted hugs from a couple of court workers, shook hands with the security guards and autographed baseballs for fans waiting outside.

The quick end on only the second day of testimony was the second mistrial involving a superstar player accused in baseball's steroids scandal. Home run king Barry Bonds was convicted three months ago of obstruction of justice, but a mistrial was called on three more serious false-statements charges after jurors couldn't agree on a verdict.

Walton could end the prosecution by declaring that a new trial would run afoul of double jeopardy -- the right not to be brought to trial twice on the same charges for the same offense. But experts said it was unlikely that he would go that far, especially since the trial was just under way.

"Generally speaking, mistrial does not bar a trial of the defendant when the defendant requested the mistrial," said Harry Sandick, a former prosecutor who now defends white-collar cases. He said a judge may make an exception for misconduct on the part of prosecutors, but this appears to have been a simple yet devastating mistake.

"How could the government not have reviewed each piece of evidence after the court's pretrial rulings?" he said. "This is crucially important, and prosecutors have to do this all the time."

New York Yankees star shortstop Derek Jeter, once a teammate of Clemens', said after the mistrial was declared: "I'm no legal expert, but you want it to be behind him. Obviously, the more attention that's paid to that, it's just negative for the game in general."

The U.S. attorney's office in Washington, which tried the case, said it would have no comment because of Walton's gag order. Clemens also stayed mum.

"I'm not going to say anything," Clemens said as he left the courthouse. He and his legal team ducked into a nearby restaurant to escape the media horde following him.