A shot from a BB gun fired at a rookie cop at a Brooklyn housing project led to the arrest of 15 people on gun and drug charges, police said Friday.

The officer, who escaped the Thursday night incident with a minor bruise, was patrolling Bedford-Stuyvesant's Louis Armstrong Houses with his partner when he felt a sting, police said.

The officer saw a pellet and realized he had been shot in the hat.

The officers spotted an open window on the fourth-floor of 370 Lexington Ave. and made a beeline there.

Inside the apartment, they found 15 people, a Crosman BB gun, an unloaded .358 Magnum, ammunition and crack cocaine, police said.

All 15 were charged with gun and drug possession, and Elliot Allen, 22, admitted he fired the BB gun, claiming he wasn't aiming at anyone.

Police said they believe Allen wanted to get back at the officer because he had arrested one of the men in the apartment, Tyrike Dario, earlier in the evening and gave him a summons for disorderly conduct.