The solid black flag is used to summon a driver to the pits. It is usually associated with a penalty imposed on the driver for disobeying the rules, but may also be used when a car is suffering a mechanical failure, leaking fluid, exhibiting damage such as loose bodywork, loose hood, dragging bumper, or any other damage that could potentially become a hazard to the driver or other competitors. In some cases, the black flag may be used to call a driver to the pits when their radio is not working.