Roger Federer has pretty much the same motion on all his serves right up until wrist pronation. Which means after he's tossed the ball, he can still change his mind as to which serve to hit.
Some returners take one return position, then, when the toss is made, move. They're hoping that the server will have chosen a serve optimal for their apparent return position, but they'll now be in a different position for which the chosen serve is sub-optimal.
So when Federer puts the toss up, if he hears movement at the other end of the court, he'll sometimes change his mind mid-motion as to which serve to hit. Marou also has the same motion on all his serves till late in the motion, so I'd like to see him try that. With his size, that's the sort of crazy yet subtle display of technical mastery he needs to eventually win major titles.
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