What do the flags mean in downhill, and when does a rider get a re-run?

• Marshals: each stands in direct line of sight of the next and signals an approaching rider with a short blast on a whistle.
• Yellow flag: carried by every marshal in official training and waved after a crash "to warn other riders who must slow down".
• Red flag: carried by selected marshals with radios, in training and in racing.
• Passing it down: a red-flag marshal who sees a colleague further down the course waving the flag must do the same at once.
• The rider's duty: "Riders observing a waving red flag during the race must stop immediately."
• Afterwards: the rider must "continue calmly to the finish and request a re-start from the finish line commissaire".
• Course walk: an inspection on foot before the first training session. No bikes.
• Training sessions: one the day before the race and one on the morning of race day.
• Two runs: "Riders must complete at least two training runs or they will be disqualified from the race."
• From the top: training runs start at the official start gate. Starting below the line means disqualification, unless the president of the commissaires' panel has named another starting point.
• Not during a race: no training while a race is in progress.

The glossary has downhill and the commissaires panel.

On a course ridden at speed between trees, a rider cannot see a fallen rider round the next bend. The chain of flags carries the warning up the hill faster than a rider travels down it. Compulsory training runs make sure nobody meets the course for the first time at race pace.