One out of three of the people like soccer. In my point of view, there are just only football match are the same Olympics that settle every 4 years competition.
There are hundreds of millions, if not billions of football/soccer fans around the world. I can't remember exactly where I read it, but something was said about an estimated 2 billion people tuning in at some stage of this years World Cup. Now that in itself is a crazy figure for a single sporting event. But yes, of course, football is the most popular and most supported sport in the world going on numbers. That's well known.
Football what do you exactly refer to? Because like here in United States, Football (NFL/NCAA) is where the players is throwing the object or are you talking about football as in Soccer where the players kicks the object (united states word) in other countries?
I think it's pretty safe to say that at least a fourth of the entire world's population? Football is HUGE, especially if you consider the fact that there's american football, soccer, Australian football (WHICH IS AWESOME) and probably other kinds of football nobody's really even heard about. ahaha
How accurate does the answer need to be? What will you use the statistic for? winning a drinking game?