From the same article:
In one incident Tuesday, on the steps of the New York Public Library, protesters who were not trying to cause any disturbance - though they did not have a permit - ended up in a 15-minute melee with police, prompting rows of officers in helmets, clubs in hand, to form a phalanx on the steps. The officers moved in unison, chanting "Move, move, move." One uniformed officer swung his club wildly at protesters and at journalists, trying to force them back.