Police hauled in a crazed 23-year-old man Sunday accused of terrorizing his elderly grandmother and assaulting a cop coming to her rescue.

When cops stormed the home in the Sunnydale housing projects around 9 p.m., they said the lunatic was out-of-control. They described his 87-year-old grandmother, who had called police, as “cowering and terrified.”

Police tried to handcuff the “erratic” and agitated man, who resisted and injured one of the officers.

Cops found he had a warrant for his arrest and booked him into county jail. His identity was not immediately available.

“His grandmother ... had been living in constant fear of him,” police said.

Adult Protective Services was notified of the incident, police said.

maldax@sfexaminer.com