Red flag

A red flag stops the session outright: cars slow immediately and form up, either on the grid or in the pit lane, until conditions allow a restart. Race control reaches for it when marshals or medical crews need a live-free track, or when weather makes racing impossible.

The endurance-specific detail is the clock. A 6-hour or 24-hour race runs to time, not distance, so every red-flagged minute is racing that never happens. A long stoppage at Le Mans effectively shortens the race, and restart order and procedure follow the sporting regulations rather than simply resuming the old gaps.