What is the term for a disqualifying early start in drag racing?

The term for a disqualifying early start in drag racing is a red light.

Drag racers start from a “Christmas tree,” the vertical light system positioned between the lanes. After the staging lights are set, amber bulbs count down toward green. If a vehicle breaks the starting-line beam before the legal start, the red bulb illuminates for that lane and the driver is charged with a red-light foul, commonly called a red light.

The rule is designed to penalize a driver who leaves early while preserving the importance of reaction time. In many heads-up starts, the opponent does not need to complete the run: making a legal pass is normally enough to win after the other driver commits the foul. A red light is not literally the green light appearing late; it identifies the early departure.

The other colors have different jobs. Amber lights provide the countdown, green signals a clean start, and blue lights indicate pre-stage and stage positions. Exact procedures can vary with the starting tree and race format, especially when both drivers leave early.