Crowds of young people caused chaos coast to coast over the Memorial Day holiday weekend.

In Hollywood, Florida, nine people were shot on Monday. The violence reportedly started with several young men fighting when one of them pulled out a gun and started shooting.

It was a scary scene to roll into,” said Hollywood Beach resident Jamie Ward to Sinclair station WPEC. “To really see it first hand, everyone was mortified.”

Another tragic scene unfolded on Monday in Revere Beach in Massachusetts. Police detained several juveniles in connection to a shooting. Officials say shots were fired into a group of young people during a fight.

In San Clemente, California, three off-duty Marines were reportedly attacked by nearly 40 teens on Friday.

Last week a festival in Tinley Park, a suburb outside Chicago, was canceled for safety concerns following a chaotic flash mob involving hundreds of teens.

Federal data shows this type of youth violence started trending upwards in 2020, when homicides committed by multiple juveniles rose 66% compared to the year before.

"In the post-COVID world we are definitely seeing more of this," said Jason Johnson, president of the Law Enforcement Legal Defense Fund. "Whether it’s being driven by whatever happened to young people during COVID is not for me to say but you know a long period of time being out of school, out of a structured environment, and you just have to wonder what impact that had on young people."

Johnson also pointed out that police shortages and a reduction of penalties for juveniles who commit crimes likely also contribute to the increasing frequency of youth mob violence.

With the school year ending, law enforcement agencies are bracing for what the coming months may bring.