A slang term referring to the referees. The name is derived from the fact that the referee jerseys are black and white stripes.
Lloyd Olds, a college referee, is credited with inventing the striped jersey in the 1920s. Previously football referees wore white dress shirts, knickers, hat, and black stockings. In 1945 the black and white striped jersey became standardized across professional football.
The official's hat also doubles as a piece of equipment, if player steps out of bounds (without the ball) the official will drop his hat on the ground. The hat can also be used as a penalty indicator if he's already thrown the yellow flag for another infraction.