I think there is at least two parts to this: 1 - what is actually going on and 2 - what it feels like, what I cue to get the correct motion.
For 2 - thinking about the arm has resulted in me strong arming the disc and I get noticeably more power the more I can just whip and keep the arm loose.
For 1 - I think it is mostly about shoulder protraction (retraction will invariably result in bad rounding). When loading the disc behind you like in the door frame position while keeping the shoulder protracted the disc is gonna whip into the pocket and out of it without rounding going on.
However, maybe something else is going on, thus the question to which degree he might be driving the elbow forward consciously (
arming it) vs. just keeping it loose and it whipping around. The screenshot below shows Courtis in the doorframe position, do you think he drives the elbow forward from that position or is he whipping it while keeping his arm loose?
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