Updated

The police chief in Rochester, N.Y., says officers showed "tremendous restraint" while subduing a teenage boy and his sister during an arrest that was videotaped and posted on YouTube.

The video was shot Tuesday by the son of a neighbor. It shows the 21-year-old woman resisting an officer's efforts to cuff her hands behind her back as she repeatedly tells him she's pregnant. While other officers are trying to handcuff her 16-year-old brother, the officer hits the woman in the head and takes her to the ground.

Police Chief James Sheppard says officers were trying to arrest her brother following a family dispute when the woman pointed a can of pepper spray at them.

Sheppard says the officer's actions during the arrest will be investigated.