The protesters gathered at various locations, many with the goal of descending on the convention site at Madison Square Garden. But at the various staging areas - near Ground Zero, in Union Square, in Herald Square near Macy's, and outside the New York Public Library - the police began making arrests, sending the crowds into a frenzy. These confrontations followed several other events, some of which went of without incident with the police taking aggressive action to prevent disruptions.
Q : Could you explain why "of" was used in the sentence?
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