This is endlessly repeated on here but it's so clearly rubbish. That would mean 7.5% of the entire human population is a Manchester United fan. If half the total human population is a football fan, that means 15% of all football fans support Manchester United. Again, tremendously unlikely, considering there are at least three other big clubs with very similar reach and following, and a number of almost-as-big clubs.
Not to mention that assuming that half the global population is interested in football is almost definitely flat-out wrong: FIFA claims the last World Cup final, the most viewed event in football, was watched by 'almost' 1.5 billion people. That's a record. There's no reason to believe that there are vast numbers of people who are usually interested in football but didn't watch the World Cup final - I'm sure there were some but I'm also sure they were outnumbered by those who usually don't give a flying feck about the sport but still watched it because it's the effing World Cup final.
Yeah, it's not very important or relevant to the thread but come on. 1.5 billion people watch the World Cup final but there are 600 million Manchester United fans? No.