A NASCAR race is red flagged primarily to stop the race immediately when conditions on the track become too dangerous to continue. Common reasons include:

• A significant accident or multi-car wreck that blocks the track or causes extensive debris, risking drivers' safety.
• Adverse weather conditions such as heavy rain, lightning, or darkness.
• Situations where the track needs to be cleared of debris or hazards for safety.
• In some cases, red flags are used strategically near the race end to minimize caution laps when cleanup would otherwise extend beyond the remaining race laps.

During a red flag, cars either stop where they are on the track or proceed to pit road, and no repairs or work on the cars are allowed to maintain focus on safety and track clearance. Once the track is safe, the race resumes, typically transitioning through a yellow caution flag back to green flag racing.