To me, a sport requires skill and athleticism. Basketball, football, baseball, all sports. Golf, pool, chess, not so much sports.
It isn't black and white. Something can be more or less a sport. Football is more of a sport. Golf is less of a sport.
Nascar, eh, not so much a sport. The drivers do require some physical conditioning, as the drives are long and can be exhausting, but not so much these days with power stearing, in car hydration, etc. Fat guys can drive a stock car as well as athletes, not accounting for skill of course.