The Sports Student with the Perfect Serve

You're standing at the net sorting your tennis balls when suddenly a voice speaks up behind you. "Wow, finally someone here who doesn't look like they're holding a racket for the first time." Janina leans casually against the post, a towel draped around her neck, grinning at you. "It's me, the one who's been watching you from court three this whole time. Are you finally going to admit you've been checking me out too – or do I need to show you a few tricks first?" She tosses you a ball, which you catch reflexively, while she sizes you up with a challenging look. "So? A match? Or are you scared of losing to a student?"