United States v. Clyde was a United States Supreme Court case that dealt with the issue of whether a person could be convicted of a crime if the evidence was obtained through an illegal search and seizure. The case involved a man named Clyde who was accused of stealing a horse. The police searched Clyde's house without a warrant and found the stolen horse. Clyde was then arrested and charged with the crime. The Supreme Court ruled that the evidence obtained through the illegal search and seizure was inadmissible in court and that Clyde could not be convicted of the crime. The Court held that the Fourth Amendment of the United States Constitution protects citizens from unreasonable searches and seizures and that any evidence obtained through an illegal search and seizure is inadmissible in court. This ruling established the exclusionary rule, which states that any evidence obtained through an illegal search and seizure is inadmissible in court. The ruling in United States v. Clyde was an important step in protecting citizens from unreasonable searches and seizures and in ensuring that the Fourth Amendment is respected. The exclusionary rule established by this case is still in effect today and is an important part of the criminal justice system.

In United States v. Clyde, the Supreme Court was asked to decide whether a conviction for selling liquor without a license in violation of an act of Congress could be sustained when the indictment did not allege that the defendant knew he was violating federal law. The majority opinion held that knowledge of unlawfulness is not necessary to sustain such a conviction, and thus affirmed the lower court's decision convicting Clyde. However, Justice Field dissented from this ruling on several grounds. He argued that ignorance or mistake as to any fact which would make an act criminal should always be taken into consideration by courts in determining guilt or innocence; therefore, since there was no allegation in this case that Clyde had knowledge of his violation being illegal under federal law, his conviction should have been overturned. Additionally, Field asserted that it is unjust and oppressive to punish people who are unaware they are breaking laws enacted by Congress due to their lack of access or understanding regarding those laws' existence and content; thus he concluded with urging caution against punishing individuals for acts done innocently out of ignorance rather than maliciously out of willfulness.