In the United States, jury nullification occurs when a jury in a criminal case reaches a verdict contrary to the weight of evidence, sometimes because of a disagreement with the relevant law. It has its origins in colonial America under British law. The American jury draws its power of nullification from its right to render a general verdict in criminal trials, the inability of criminal courts to direct a verdict no matter how strong the evidence, the Fifth Amendment's Double Jeopardy Clause, which prohibits the appeal of an acquittal, and the fact that jurors cannot be punished for the verdict they return.
In practice
The tradition of jury nullification in the United States has its roots in the British legal system, specifically in a 1670 English case where Quakers were acquitted by a jury of violating a law that permitted religious assemblies only under the Church of England. In 1735, journalist John Peter Zenger was acquitted in New York by a jury that nullified a law making it a crime to criticize public officials. Later, colonial juries nullified the Navigation Acts, which would have forced all trade with the colonies to pass through...