U.S. law defines police brutality as the use of more force than necessary to apprehend or subdue a civilian. "Excessive force" has no precise definition and is determined in a court of law by asking whether more force was used than a "reasonable and prudent law officer would use under the circumstances." Individual states also have their own laws against police brutality.
The Fourth Amedment
Courts commonly use the U.S. Constitution's fourth amendment against unreasonable search and seizure in police brutality cases. The fourth amendment guarantees freedom from unreasonable search and seizure. Judges and lawyers argue that the Constitution writers did not want law enforcement officers causing unnecessary harm to citizens. The Supreme Court has stated that the term "reasonable" also implies that different situations require different amounts of force and therefore that excessive force should be avoided.
The Constitution's fourteenth amendment says, "No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty or property without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws." The "due process" clause guarantees that citizens appear before the judicial system. Excessive force violates that right by effectively punishing citizens before they are tried.
Federal law limits the times the police may use force. Law enforcement officers may only use force to protect themselves, other citizens or to protect public order. Police use the right to employ force to protect public order when a citizen simply refuses to cooperate with the police.
Civil Rights Act of 1871
The Civil Rights Act of 1871 was initially written to protect freed African-Americans in the south from the Ku Klux Klan. It makes it illegal to interfere with any of the rights guaranteed by the Constitution. Since the fourth and fourteenth Amendments limit the use of force, the Civil Rights Act is useful in cases against police brutality.