Law enforcement officers that respond to the scene rarely get the full story from both of the parties and all the witnesses. The police are often left to confront contradictory statements, and they then sometimes jump to conclusion about the true version of events. In many of these cases, no physical evidence of any injury is present. The officers rarely know much if anything about the past difficulties of the parties.
In many cases, drugs or alcohol makes the statements from witnesses and suspects less than reliable. Under the difficult circumstances, the police must make an arrest. Sometimes they will even tell the suspects that since the police were called, “Someone is going to jail.” Sometimes the police make a mistake, but that mistake still has unfortunate consequences for the person arrested.