Serena Williams, the best women’s tennis player in the world, may have lost her cool and the US Open final, but it was sparked a much needed debate on sexism in sport. Serena called the umpire a liar and cheat for docking her a point after two code violations. Did she cross the line? Perhaps she did. But the firestorm is raging over another question - would the referee have been as strict if he was dealing with a male player? The world of tennis is divided.