So gopniki gop stop somebody (though they don't like the term, they prefer pacani or sth else instead).
They're usually teenagers and move around in groups.
In English the closest term/translation would be "to racket". The gop stop is just not so well orginized and they have casual victims (who they call lohs - a clumsy, slow thinking person or the ones who afraid to fight back or or resist strongly).
-5 guys came up to me and asked for a phone call. They swore they had their own Sim card. A police officer told me I was simply gop stopped.