From what I’ve read about many of the 1960s “rallies”, some band would be giving a free concert in the park and some stinking socialists would take the stage (and the mike) away from the performers.
The crowds were not always gathered for political reasons. But the politicos claimed them as their “supporters”.
During The Who’s set at Woodstock, Abbie Hoffman took to the stage and grabbed Pete Townsend’s microphone, and just as he was in the middle of yelling, “Free Rubin Sinclair”, Townsend “El Kabonged” him over the head with his SG.