Penalties

Finishing a race without serving a penalty, can get you disqualified.

While the game allows to turn off some or all HUD elements, Penalty warnings are part of "Essentials" elements. Because of that, it's not recommended to turn off all HUD elements, but you can leave it at "Essentials only" to be able to see Penalty warnings and serve them in time (Settings > Gameplay > HUD > In Game Overlays).

Stop-and-go
Drive through pit with stopping, notice you have to select serve penalty in pitmenu before the pit.

Drive through
Drive through pit without stopping, notice you have to select serve penalty in pitmenu before the pit.

Slow down
You get a slow-down penalty, which must be served within a specified time period.