What is a mistrial?

A mistrial ends a trial without a verdict. Several causes.

A hung jury, described above. Retrial is generally permitted.

Prejudicial error — improper testimony, an inadmissible reference the jury heard, prosecutorial misconduct, or juror misconduct. Where the defense moves for a mistrial and it's granted, retrial is generally permitted.

The exception that matters. Where prosecutorial misconduct was intended to provoke a mistrial, double jeopardy can bar retrial. That's a narrow and rarely successful argument, but it exists.

A defense choice, not automatic. When something improper happens, the defense sometimes chooses *not* to move for a mistrial — because the trial is going well and starting over would lose that advantage. A curative instruction may be preferable.

That's a real-time strategic judgment, made in seconds, and it's one of the less visible parts of trial work.