Some clarifications and exceptions apply. If the driver is a lap down because of a NASCAR penalty he is not eligible for the lucky dog pass.
Drivers who are a lap down because of mechanical problems are not eligible for the lucky dog until the leaders have lapped at least one car on the track.
The driver that causes the caution is not eligible to receive the Lucky Dog pass during that yellow.
Why Was the Lucky Dog Rule Introduced?
The lucky dog rule was first used at Dover in September of 2003. One of the drivers to receive the lucky dog during that first race was Ryan Newman. He took full advantage of his free pass and went on to win the race.
Before the rule went into effect, there was a general understanding that when there was a caution flag, drivers would slow down and not pass slower cars when "racing back to the caution," or recouping the time they lost while the caution was in place.
After a near-miss between drivers Casey Mears and Dale Jarrett at the Sylvania 300 in 2003, NASCAR opted to implement the rule to halt all racing whenever there was an incident on the track, and the beneficiary rule allowed slower cars to catch up.
Where Did the Term 'Lucky Dog' Come From?
The first person to call NASCAR's beneficiary rule the "lucky dog" rule was Benny Parsons, who was calling a race in 2003 at Dover International Speedway. The term was quickly adopted by most (but not all) broadcasters. The term conveys the skeptics' view that the rule gives an unfair advantage to an undeserving driver, but in the vernacular of NASCAR.
Is the Lucky Dog Rule Fair?
Critics of the rules say it provides an arbitrary advantage to a driver that doesn't deserve it because the driver hasn't done anything to earn it. He doesn't have to be within a certain distance of the leader or earn it based on drivers points or anything else. Just be the first car one lap down, have a yellow come out and you get the free lap.
There have been a number of occasions where a driver took advantage of the lucky dog rule and came back to win the race. Ryan Newman has the dubious distinction of winning two races as the lucky dog, at Dover in 2003 as mentioned above, and at Michigan in 2004. Kevin Harvick won at Daytona in 2010 after a lucky dog.