New trial for Roger Clemens?

The judge in the perjury trial of former New York Yankees pitcher Roger Clemens declared a mistrial Thursday, after prosecutors showed jurors evidence the judge had ruled out-of-bounds.

Federal prosecutors were under strict orders not to mention Laura Pettitte, the wife of former Clemens teammate Andy Petitte, because the judge ruled her testimony was secondhand and inadmissible.

So when prosecutors played a tape of members of Congress discussing Laura Pettitte's testimony, Judge Reggie Walton erupted, calling it "prejudicial" against the former baseball star and a "direct violation" of his order.

George Washington University Law School Paul Butler explained, "The judge said the jury's not allowed to hear this evidence, the prosecution went ahead and let the jury know about it anyway. So it's a big deal."

CBS News Correspondent Wyatt Andrews reported the judge all but accused the prosecution of cheating. The judge, at one point, told prosecutors, "Government counsel can't do what it thinks it can get away with. Any first year law student should know that."

Clemens will now argue all charges should be dropped, based on constitutional bans on double jeopardy -- two trials for the same offense. Legally, it's a long-shot, but a hearing is set for Sept. 2.

So what are the chances of the case being retried?

CBS News Legal Analyst Jack Ford said the judge will base the decision on the severity of the offense.

He said, "If a judge believes that a prosecutor did something intentionally -- there's some sinister motive here. We've seen it in some cases -- not a lot -- but a prosecutor buries evidence that could have been exculpatory or they coach a witness to say something when they know they're not supposed to be saying (it). In those situations, a judge can step up and say, 'You know what? This is so egregious here, I'm not going to let you do this over again."'

Ford continued, "The question becomes, though, if it's inadvertent, but grossly inadvertent, would that be enough for a judge to say -- and this is going to be a real issue for the judge now -- is that enough for a judge to say, 'You had your shot. You blew it, and I think it's really your fault that you blew it, and it was so serious that I'm not going to subject, in this case, Mr. Clemens to another trial.' The judge will have to wrestle with that decision. We'll know something back in September."

A mistrial, Ford said, is an unusual court outcome. He explained, "Essentially, it happens if a judge believes something has played out in front of the jury that could have an impact on the integrity of the trial."

A mistrial can happen, Ford said, in cases when jurors speak to other people during a trial, do their own research, or if a witness blurts out something they shouldn't, among other situations.

Ford said, "More often than not, judges are able to instruct jurors, 'Just ignore that, make believe it didn't happen here,' but when it gets to be so important, the judge says, 'This is way too prejudicial. As a consequence, this trial is over."'

Ford said the judge and the prosecution had argued about Laura Pettitte's testimony, but it was thrown out as hearsay. So when the tape was played for the jury, Ford explained, "The judge said, 'Look, this was clear, this should not be a problem, I ruled this is not coming in and it showed up anyway, so this is done."'