The two Bludgers are round, jet black balls, made of iron. A Bludger is 10 inches (25 cm) in diameter. They are described as being bewitched to fly without any visible means of propulsion, although they do retain inertia, which makes them unable to change speed or direction swiftly. They act as airborne obstacles, flying around the pitch and trying indiscriminately to knock players off their brooms.