Detroit slang for a group of African-American police officers who support or reinforce a group of white police officers.
Two white cops are writing a parking ticket outside a night club when a dozen black men rush out the door yelling and fighting one another. The cops immediately call for help on the radio. Minutes later, two cop cars with four big, black cops arrive.
Observer 1: "Wow, those white cops were in over their heads."
Observer 2: "Yep. That's why they called for blackup."