The term legal technicality refers to the technical niceties and exactitudes of legal procedure, defensess based on such technicalities are known as "procedural defenses". It is often used in a pejorative sense to denote aspects of legal procedure which, if not attended to or followed, can change the outcome of a legal proceeding in ways seemingly contrary to the interests of justice. Some legal technicalities restrict access to courts and legal procedures or limit the discretion of a court in handing down judgment. In almost every case, well-established technical aspects of legal procedure have come into being and have been reinforced in a long tradition of appellate court decisions because of a perceived need to protect the rights of a class of persons who might otherwise suffer injustice at the hands of the legal system.
Constitutional guarantees such as those included in the Fourth and Fifth amendments to protect an accused from unreasonable search and seizure or from self-incrimination are sometimes referred to as "technicalities" by critics of court decisions based on them, even though they are foundations of the American legal system rather than obscure fine points. A commonly cited example would be attempted prosecution of a crime that was discovered by illegally obtained evidence. Such cases may be dismissed based on lack of evidence as the illegally obtained evidence would not be allowed to be the basis of the prosecution's case.
Some examples of technical aspects of legal procedure are: