In the United States, a judge can alter or reverse a jury's decision in certain instances. A guilty verdict may be reversed in the event of insufficient evidence from the prosecution. Overturning a verdict is known as a judgment of acquittal or a judgment notwithstanding the verdict.
Overturning a verdict may happen when a motion is filed by the defense to the presiding judge. The motion is almost always denied, but the defense can file an appeal. If the judge reverses a verdict, the evidence must be examined in a manner that leans toward the prosecution. If the evidence doesn't determine guilt, the judge is compelled to reverse the guilty verdict. A judge typically doesn't overturn a not guilty verdict, because doing so would violate the Sixth Amendment of the U.S. Constitution. Reversing a not guilty verdict also negates the purpose of having a trial.