How do you define big? Clearly not most athletes, as then F1 is not an option. Most money involved?
For number of people performing the sport more than just for leasure, I believe Volleyball is the biggest. But there's not a whole lot of money in it.
I guess I was going for any combination of factors really, whether it is professional or recreational participation, TV ratings, money and advertising etc. Basically which ever factors people view as most important. I understand that this is incredibly subjective and am interested to see how people view this.
I personally would give the silver medal to basketball and bronze medal to athletics/track and field.
I think overall volleyball would comfortably be in the top 10, at least. There are some professional leagues across Europe, the Far East and of course Brazil where it is the second most popular sport behind football. Of course for men a lot of other sports would pay a lot more. I think for women though, the pay in those leagues might be pretty good compared to a lot of other sports.
Its Olympic status was certainly hurt thanks to being played in relatively few countries, but many of the countries that do play it have massive population; it's clearly a more popular game overall than several niche sports that remain in the Olympics only because they're played all over the world. And I didn't follow the Olympics ejection closely (I don't care about the event in the slightest), but I do remember hearing that politics/Anti-Americanism played a part in the decision.
I don't like baseball at all (I follow the NHL, NFL and NBA but can't stand the MLB and pay no attention to the LMB here in México), but I think that it should still be an olympic sport. I do think the IOC and decision making is heavily European dominated.
Handball is a heavily European dominated sport, but I think deserves to remain an olympic sport (it is a lot of fun to watch), as does baseball. I guess some other problems are the whole baseball for men/softball for women scenario (the IOC prefer a more integrated set-up for men and women). Also I the olympic baseball movement traditionally hasn't received a lot of the support overall from MLB officials and players, which hurts a lot.