Law & Order (1990)

Answer: A courtroom trial that has been terminated prior to its normal conclusion. A mistrial has no legal effect and is considered an invalid or nugatory trial. This often happens when there is a lack of Jurisdiction, an incorrect jury selection or, as seen in many of the episodes, a hung jury, i.e. some jury members finding the defendant guilty while the other members of the jury will find the defendant not guilty and all jury members won't change their decision.

Answer: I was once a juror on a trial where the defendant started crying and talking about how his son would suffer if he went to jail. The judge became furious, decided that he had prejudiced the state's case (we were now thinking of his family, rather than if he were actually guilty), and declared a mistrial.

Brian Katcher

Answer: In short, any time a trial ends and is declared void before the jury delivers a verdict or a judge issues a decision. Generally a mistrial is caused by a jury not being able to come to unanimous decision or the prosecution does something that would make the trial unfair to the defendant.

Bishop73