The Kentucky Derby is the number one horse spectator sport in the US. It is a prestigious horse race held annually in Louisville, Kentucky, and is known as "The Most Exciting Two Minutes in Sports."
Football.
Rodeos
Soccer- worldwide Football- U.S.
Yes, NASCAR is the 2nd most popular spectator sport in the U.S. behind the NFL.
The NFL and College Football are really popular sports watched in the USA. Football is the most popular spectator sport in the US.
The sport is embraced heavily by the US and is played in nearly every school (high school and college) in the country. American football is one of the biggest spectator sports in the US and by far has the best Pro/League to play the game. To the US, American Football is the spectator equivalent to "proper football"/"Footy" and/or Rugby for most other countries in this world. Not to mention, nearly every other country in the world just don't embrace the sport.
Nascar ran a series of races called the Grand National. It was a precursor of what is the largest spectator sport in the US today.
Considered by some as a sport but not all, the Nascar Circut draws more in attendance than any other competitive sport. American football is second, followed closely (due to the length of the season) is baseball.
It would help us greatly to know which sport and/or league you are inquiring about.
Well football is the number one sport of all time and Nascar is kind of lower than football. So it would be football.
It is American football even though it is number one in America, and growing in popularity outside the US, soccer is still the world's best sport.