In this photo, Petra Kvitova sets up to hit her two-handed backhand in a mostly open stance. For most players, especially below the pro level, a two-hander is much easier to hit in a square stance
, but by coiling her upper body as you see here, Petra can generate more power as she uncoils with the swing. Her shoulders are coiled 90 degrees in relation to her hips, and her racquet is laid back another 45 degrees or so from her shoulders. Petra's strong knee bend prepares her to generate a powerful upward thrust with her legs as she uncoils.