American policing does not appear to have benefitted from psychological insights! In a recent edition of New Scientist (30 August) Michael Bond reflects on the body of research that has shown that crowds are not mad, bad and dangerous. They are often happy collections of people (think Glastonbury). Even demonstrations often have a fairly carnival-type atmosphere with everyone sharing a positive energy.
However the dynamics of a crowd may swiftly change when members feel threatened. The crowd may respond as one if they perceive a threat to any individuals. This is the social identity model of crowd behaviour promoted by, for example, Stephen Reicher of St Andrews University. Police in the UK and Europe generally have taken this message on board. For example, in the UK police field liaison officers in blue bibs to interact with the crowd from within and build rapport.
The more traditional methods of crowd policing, still used in America, are much more militarised. The police put on a show of force and try to contain a growing menace – a menace which in some sense is created by the policing methods. Long live psychology!