After years of being one of the top sporting attractions in the U.S., in terms of attendance per event, the NASCAR Stock Car circuit began to languish as the novelty of seeing cars with a passing resemblance to the family sedan go very fast and turn left for several hours waned.
Taking a page from the playbook of other professional sports leagues, NASCAR divided the season into two segments, essentially creating a stock car playoffs series. After the first 26 races of the season, the top 16 drivers in terms of point totals take part in the Chase for the Sprint Cup. This scheme was instituted in 2004. The last major change to the format took place in 2014, when the number of drivers and cars qualifying for the final 10-race series was raise from 12 to 16.
There is also a tiered system in place that divides the Chase into four rounds. The top 12 finishers in the first round move on to the next. By the time the fourth round comes along, the final race of the season features the top four. The highest finisher of the top four in the last race wins the Sprint Cup.
The unique aspect of the series is that even cars and drivers that did not qualify for the championship still participate in the race.
Think of an AFL Grand Final between the Cats and the Swans being played simultaneously while the Crows played the Kangaroos.