"This study is concerned with injuries that may occur to police officers and citizens during use of force events. Previous research has shown that a very small (1-2) percentage of police-citizen contacts involve the threat or application of physical force by the police, while 15-20 percent of arrests may result in the use of force by police to control a suspect. While most uses of force are low level, and involve officers' hands, arms, and bodies to gain control of a suspect, some applications of force are more serious, including less lethal devices such as pepper spray, batons, or Tasers, as well as the use of firearms. Various legal and policy restrictions govern the use of force by police, beginning with the 4th Amendment's prohibition against unreasonable searches and seizures and devolving downward to state statutes and departmental policies that govern how and under what conditions officers may use force. In most law enforcement agencies today, the use of force is tightly controlled by policy, and more serious applications of force are reviewed and/or investigated by supervisory personnel or internal affairs units."
National Institute of Justice (U.S.)
National Criminal Justice Reference Service: http://www.ncjrs.gov/