A knife-wielding nut with a lengthy rap sheet pummeled two NYPD cops after smashing the window of their police car Tuesday in the Bronx, law enforcement sources said.

Patrick Young, 34, allegedly ran up to a cruiser with a pair of cops sitting inside while holding a large knife at around 5 p.m. in front of Brothers Police and Security store on Webster Avenue in Bedford Park.

Young dropped his knife and then flew into a rage — allegedly punching the driver’s side window repeatedly and causing it to break.

The cops got out their cruiser to confront Young, but he socked them both as they tried to slap cuffs on him, according to sources. 

Police eventually took out a Taser and ordered Young to the ground, resulting in his arrest, the sources added. 

Young — who has more than 20 prior arrests — was taken to St. Barnabas Hospital for a psychological evaluation and cuts to his hand. 

Young, of the Bronx, was charged with assault and criminal mischief. 

One of his recent arrests was for menacing with a weapon, police sources said. 

The two officers, meanwhile, were treated for contusions and scrapes at North Central Hospital, according to sources.