A diagonally divided black-and-white flag is displayed with a car number to indicate a penalty for unsportsmanlike conduct. This flag can be displayed if a car tries to intentionally drive another car off the course, or if a driver gets out of his or her car and initiates an altercation with another driver.

Some administrators (NASCAR and IndyCar) do not distinguish mechanical problems or unsportsmanlike conduct from rules violations and simply use the solid black flag for all violations. Wikipedia