Definition - What does Mistrial mean?
A mistrial occurs in a trial when the trial ends for non-standard reasons such as a procedural error, prejudicial statements of those involved, or a deadlock by the jury. If a mistrial is declared, the jury is dismissed and the trial is started over from the beginning.
Justipedia explains Mistrial
In order to decide whether a mistrial should be called, a court must determine whether the error that was committed during the trial was so prejudicial that further expense and time devoted to the trial would be wasteful.