The flag language
Flags are racing's oldest communication system, now doubled by LED panels and cockpit lights. Yellow means danger — slow down, no overtaking (double yellows: be ready to stop). Green clears the hazard. Red stops the session entirely. Blue tells a lapped car to let the leaders through, and the black-and-white flag is a warning for unsporting driving — football's yellow card.
The checkered flag needs no explanation, though it has been shown early by celebrity flag-wavers more than once, with chaotic results.
Safety Car and Virtual Safety Car
When a hazard needs marshals on track, race control deploys the Safety Car. The field bunches behind it at reduced speed, gaps evaporate, and pit stops suddenly cost half as much time — which is why a well-timed safety car can flip a race on its head.
The Virtual Safety Car (VSC) achieves the slowdown without the bunching: every driver must stay above a reference 'delta' time, roughly preserving the gaps. Introduced after Jules Bianchi's 2014 accident, it's used for smaller hazards.
Red flags and restarts
A red flag suspends the session: cars file into the pit lane and wait. During the stoppage teams may change tires and repair damage — a free reset that has rescued races for some and stolen them from others.
Restarts happen either as a rolling start behind the safety car or a full standing restart from the grid, at race control's discretion. A late red flag effectively creates a sprint to the finish.