A man who violently shook his toddler and then threw the girl in front of a moving car was arrested by an off-duty Oakland police officer who witnessed the incident and hailed a citizen's vehicle to help chase him down, police said Sunday.

The officer, whose name was not released, was off-duty and on foot when he saw a man later identified as John Taylor Jr., 21, yelling in the middle of Fifth Avenue near East 15th Street around 5:40 p.m. Saturday.