In enforcing laws and in dealing with many routine situations, such as family quarrels and large sidewalk gatherings, police must often use their own discretion. Usually they must decide for themselves whether the behavior of a person or group is disorderly, suspicious, or threatening enough to require police intervention. They must also decide how to intervene most effectively and without violating an individual's legal rights.

Many police procedures—especially those related to the search, detention, and questioning of suspects—conform to rulings by the U.S. Supreme Court and other courts of appeals. Rulings that have especially affected police work include those designed to protect rights to privacy, free speech, peaceable assembly, counsel, freedom from arbitrary search and seizure, and avoidance of selfincrimination.

In some cases, such as curfew violations by juveniles or certain forms of illegal sexual conduct, police may feel that an arrest would be unwarranted or ineffective. Sometimes the community itself does not support strict law enforcement in cases that involve juveniles or regulation of morals. In cases involving prostitution, gambling, narcotics use, violation of liquor laws, or extortion, legal evidence to justify an arrest may be very hard to gather.

Police may be called on to enforce highly unpopular laws, either acting against behavior or conditions the community approves or protecting those it opposes. They may have to confront behavior or conditions that seriously offend the community but are not clearly illegal or disorderly. Examples have included strikes, protests, and demonstrations. Police must often weigh the potential threat to the community, anticipate public reactions, and interpret the laws that may apply.

It is generally accepted that police have the authority to use force when necessary in carrying out their enforcement and protection duties. Police officers must decide when the use of force is justified and how much force is appropriate. The use of excessive force is known as police brutality. Although police brutality has been identified as a serious problem since the 1960s, in the 1990's a number of highly publicized court cases concerning police brutality heightened the public's awareness of the issue.