Explain stop and frisk as a police technique

Stop-and-frisk is a highly controversial technique used by police to combat crime. It involves a brief, non-invasive search of a suspect believed by the police to have committed, or about to commit, a crime. The police officers must have reasonable suspicion before conducting a search. Reasonable suspicion cannot be used to conduct a full body search; it must only be used to justify brief stops and detentions. And any searches carried out under stop-and-frisk must comply with the Fourth Amendment.
Nonetheless, the stop-and-frisk procedure still gives the police a fair amount of discretion in conducting searches. A fierce debate has raged as to whether stop-and-frisk is truly effective, and furthermore whether it unfairly targets minority suspects. Critics argue that that it amounts to racial profiling: identifying criminal suspects according to their race rather than what they might have done.
The available evidence suggests that the main problem with stop-and-frisk is not so much with the procedure itself, but how it's used in practice. For all too often those stopped by police tend to be disproportionately from minority groups. In New York City, for example, a New York Times article reported that 83% of African-American and Latino males had been stopped and frisked despite collectively constituting just over 50% of the city's population. It seems there's too often a temptation for police officers to allow either their experience or, in some cases, their prejudice, to influence their use of stop-and-frisk.
Interestingly, a U.S. District Court judgement in 2013 ruled that though the practice of stop-and-frisk was not in itself unconstitutional, it had been carried out in a way that violated suspects' constitutional rights. Nevertheless, the court's verdict was enough for the NYPD to discontinue the use of stop-and-frisk not long after.
 
 
https://www.factcheck.org/2016/09/is-stop-and-frisk-unconstitutional/