In the Roger Clemens trial yesterday, the prosecution introduced evidence regarding Laura Pettite that Judge Walton had previously ruled was inadmissible. That was a no no, because once introduced, Judge Walton concluded that Clemens couldn't get a fair trial. So that was it, and a mistrial was declared.
So the issue now is whether, after the prosecution dedicated lots of tax dollars and time in preparing for the trial, will there be a retrial (or a new trial).
Your starting point is the double jeopardy rule which arises from the Fifth Amendment in the U.S. Constitution. It says a person can't be tried for the same crime twice. Here's an important point - if the jury didn't reach a verdict, a retrial could still happen.
In figuring out whether there will be a retrial, the Court will look at things like whether a retrial would result in unfair delays for Clemens, whether the prosecution would secure an unfair advantage for the prosecution and whether the prosecution did all this on purpose.
The Clemens case just started and there have been no surprises so far. It is a strained argument that the prosecution would gain some type of advantage by getting a retrial or hitting the reset button. The trial is also only 2 days old, and a new trial could get underway by October, although it could be later. So delay doesn't seem like a big issue.
Overall, the reasonable conclusion is that there will be a retrial.
That being said, this case has been a little strange and unpredictable. So anything could happen. Anything shouldn't happen, but it could.