Chase for the Nextel Cup

The NASCAR playoffs is a championship playoff system used in the NASCAR's three national series. The system was founded as 'The Chase for the Championship' on January 21, 2004, and was used exclusively in the Monster Energy NASCAR Cup Series from 2004 to 2015. In 2016, NASCAR implemented a version of the Chase system in the Xfinity Series and Camping World Truck Series.

The NASCAR Cup Series version of the playoff system is often called the Chase for the Cup, and includes sixteen drivers that compete for the championship in the final ten races of the Monster Energy NASCAR Cup Series. The first nine races are divided into three rounds, with four participants being eliminated after each round. The Xfinity Series Chase format is competed over seven races with twelve drivers. The Camping World Truck Series Chase also is seven races long, but only includes eight drivers.

On January 23, 2017, NASCAR announced that they will not be using the word "Chase" which would be replaced by the word "Playoffs".

The publicly stated purpose for the NASCAR playoff system was to make the NASCAR mid-season more competitive, and increase fan interest and television ratings. The timing coincides with the commencement of the college and National Football League seasons and Final Month of Major League Baseball Regular Season and Major League Baseball Playoffs Prior to the format, the Cup champion was often determined mathematically long before the end of the NASCAR season; a situation that existed in the lower-tier series, the Xfinity Series and Camping World Truck Series, until they received their own playoff formats in 2016.

By resetting and compressing the scoring of the top 10 (later, 16) drivers, the chances of each of those drivers winning the championship was increased, while not precluding anyone with a legitimate chance of winning. The original choice of top 10 drivers was based on the historical analysis that no driver outside the top 10, with 10 races remaining in the season, had ever gone on to win the Championship. The expansion to top 16 in 2014 made the elimination rounds possible.

...
Wikipedia