U.S. District Judge Reggie Walton made the call after just one day of testimony -- scheduling a hearing on September 2 to decide if there will be a new trial.
Here's what happened that triggered the mistrial. A video screen was left on while the lawyers had a private conversation with the judge. The screen displayed comments from Congressman Elijah Cummings at a House hearing, in which Cummings seemed to indicate Clemens was lying when he denied using HGH or steroids.
The seven-time Cy Young winner is accused of lying about taking performance-enhancing drugs in a 2008 testimony before Congress.