DOVER, Delaware - Nascar is not for the faint-hearted. Imagine driving 400 laps at speeds of over 300km/h. Usually, the slightest loss of control can guarantee a crash-marred race and can cause the red flags to come out. But potholes? Those too, apparently.The Nascar Sprint Cup race at Dover International Speedway in the US was red-flagged for 22 minutes because of potholes in the concrete track.LOOSE TAR CANNONS?The race was stopped 160 laps into Sunday's 400-lap race after chunks of the track came loose and damaged Jamie McMurray's car. Crews were not allowed to work on the cars.McMurray's plea for an exception was denied.Nascar officials and safety crews went to work on the potholes and tried to apply a quick-drying concrete mix.This is nothing new it seems though, according to reports. Cup races were infamously delayed by potholes at Martinsville in 2004 and the 2010 Daytona 500. In 2010, the Daytona 500 was only 42 laps in when the race was red-flagged for a two-hour delay for a "quick-fix" of potholes.