When something goes wrong on track, race control has several ways to neutralise the racing while marshals work. Each one affects strategy differently, and a caution at the right moment can flip a race on its head.
The full safety car
A real car (the Safety Car) comes out and leads the field at a controlled pace, with overtaking banned. The whole pack bunches up nose-to-tail behind it, so any gaps a leader had built evaporate. When the hazard is cleared, the safety car pulls in and the leader controls a rolling restart, with racing resuming as they cross the line.
The virtual safety car
The Virtual Safety Car (VSC) slows the field without a physical car. Every driver must hold to a minimum lap time (a delta displayed on their dash), so they all lose roughly the same proportion of time and the gaps between cars are preserved. There is no bunching, which makes the VSC less dramatic but fairer to a driver who had built a lead.
The red flag
A red flag stops the session completely. The key strategic quirk: while the cars are stopped, teams may change tyres for free, so a driver who had not yet pitted gets the work done at no time cost (see also flags & signals).
The cheap pit stop
This is why cautions matter so much. A normal pit stop costs around 20 seconds of track time. But if you pit while the field is slowed, everyone else is crawling too, so the time you lose in the pit lane is far smaller. A driver who happens to need a stop right when a safety car appears effectively gets one for a fraction of the usual cost. Pure luck that can decide a result (see pit stops & strategy).