A flag signal that instructs a specific driver to come off the track immediately. It can indicate a mechanical problem with the car, a rules violation, or a safety concern that needs to be addressed.
The HPDE First Timers Guide explains the dual meaning: "Displayed to all drivers: the track session must end early to take care of some problem on or near the track (e.g. a disabled car). Displayed to you only: something is wrong with your car or your driving. In either case, acknowledge that you've seen the flag with a wave to the corner/turn worker, reduce your speed, and come into the pits." The MORPCA Guide adds the specific procedure: "the flagger on the Start/Finish line or at the Black Flag Station will point the Black Flag to the car being flagged as it passes. The car number may be displayed at the Black Flag Station. The driver should acknowledge the Black Flag with a hand signal and proceed at reduced speed, with caution, to the pits where they will report to the Pit Marshal."