Most Baltimore residents, city politicians included, consider it normal to praise the police commissioner when the crime rate goes down and criticize him when it goes up. Subordinate police commanders, appointed by the commissioner, know that their job security depends upon their ability to prevent crime — especially violent crime. Absent considerable luck, however, it is impossible for cops to intercept criminals just before they strike. As a result, commanders pressure their officers to prevent violence indirectly, either by arresting potential perpetrators for gun or drug offenses, or by controlling the very movements of suspected criminals, such that they do not have the opportunity to do harm. Officers are told to generate enforcement statistics (primarily by making arrests) and to keep their designated patrol areas "under control." Constantly making arrests and controlling their assigned beats, however, requires officers to use precisely the tactics that so many Baltimore residents find offensive.