Roger Federer isn’t above some mind games going into the Australian Open, saying that defending champion Novak Djokovic may have made a mistake switching from Wilson to HEAD right before a Grand Slam: “I mean it’s tough because there’s always a factor with the weather, how do you play, day form, you know, other contenders, the pressure, now a new racquet,” Federer said on Djokovic defending the Aussie Open title. “I’m quite surprised he made a switch like this in the best phase of his career. He can for sure play good tennis, but I think when it comes down to the crunch you just have that bit of a doubt maybe, because you are not quite that comfortable with that racquet. But we’ll see what happens. It’s going to be a big test for him.”…