The number of stop-and-frisk encounters reported by the New York Police Department (NYPD), which septupled during the first 10 years of Mayor Michael Bloomberg’s administration, fell precipitously this year, apparently in response to criticism of the tactic.

Last year the NYPD made a record 684,330 street stops, which involve detaining, questioning, and (usually) frisking supposedly suspicious people, overwhelmingly blacks and Latinos, in the name of detecting and preventing crime. But in the second quarter of this year, the number of stops fell by 25 percent compared to the same period in 2011.

Citing unnamed police sources, The New York Times reported in August that sergeants conducting roll calls were no longer pushing officers to make street stops. “Cops are nervous, and supervisors are nervous,” a supervisor told the Times.

One source of anxiety: Last May a federal judge certified a class action lawsuit arguing that the NYPD routinely violates the Fourth Amendment because its stops and searches are not justified by reasonable suspicion and that the program is racially biased, violating the 14th Amendment’s Equal Protection Clause. In allowing the lawsuit to proceed, U.S. District Judge Shira Scheindlin rebuked the city for its “cavalier attitude” regarding these allegations.

Under the 1968 Supreme Court decision Terry v. Ohio, the NYPD’s stops are supposed to be based on reasonable suspicion of criminal activity, but only one out of 10 results in an arrest or summons. Most of the stops also involve pat-downs, which are supposed to be based on a reasonable suspicion that the subject is armed. But pat-downs discover a weapon only 2 percent of the time.

Police Commissioner Ray Kelly attributed the decrease in stops to a redeployment of the rookie officers who historically have been responsible for a substantial share of them and to new training practices, announced the day after Scheindlin’s ruling, aimed at teaching cops how to comply with Terry. “Obviously, there is attention and scrutiny on it,” Kelly said. “That’s really why we engaged in the new training evolution.”