Originally Posted by always_crosscourt
I do throw the non-hitting arm back now, however, and I didn't use to. Flinging back the arm never happened as a result of me thinking about it - it just came with repetition and getting better.
I've watched some super slo mos of Fed and it does appear that he keeps his left arm and hand more or less at his waist on the BH. The left arm doesn't flail backwards until the ball is long gone and it seems this movement is just for balance?