To those of us who know Quidditch from the fantasy world of the Harry Potter books, the idea of grown-ups running around a field with a broomstick clasped between their legs is a bit ridiculous. But make no mistake: this is serious stuff. The sport has its own governing body, the International Quidditch Association, that manages its rule book. And there’s also a World Cup, currently held by the United States, which has won the tournament three times. But now, there’s trouble brewing in the world of Quidditch.