For a few moments on Saturday, the confrontations between the police and the protesters just south of Union Square in Manhattan seemed fairly typical. People pushed, the police shoved and arrests were made, and in the many videos recording the protest, it was not always clear which of the three had come first.

As the police arrested a protester in the street, an officer wearing a white shirt — indicating a rank of lieutenant or above — walked toward a group of demonstrators nearby and sent a blast of pepper spray that hit four women, the videos show.

Numerous videos and photos captured the aftermath: two women crumpled on the sidewalk in pain, one of them screaming. They were temporarily blinded, one of the women, Chelsea Elliott, said.

Ms. Elliott, 25, who was not arrested, acknowledged that “there were some rough people out there” at the protests. She and the other women were penned in behind police netting meant for crowd control. But, she said, neither she nor the women around her did anything to warrant having pepper spray used on them.