If you are talking about American Football (NFL Gridiron) and auto racing, the answer is racing. If you are talking about Football (soccer) then its king.
NFL Gridiron is only widely watched in the US. Auto racing is watched worldwide, with Formula 1 as the worlds biggest, being huge outside the US.
Football (soccer) and F1 racing are huge outside the US, however NASCAR rules in America, TV numbers of NASCAR's Daytona 500 or Indianapolis 400. F1 dwarfs Nascar throughout rest of the world and also latin America with the largest country Brazil dominated by F1 and home to a major Grand Prix.