The preparatory stance of quarterbacks: can someone explain the physics?

Factual Questions
1

See subject.

I know the extended arm has to with the centripetal force necessary for the spine roll-which-rolls-the-shoulder-which-rolls-the-hand, but I don’t know how to say it, and I’m sure other elementary principles of physics can be educed.

Pitcher’s crouches and bowler’s approaches just before release come to kind.
ETA: Not for the first time, allow me to thank SD for giving me the opportunity to use a fancy word I don’t think I’ve ever said or written. What’s weird is I didn’t set out to do it, it just got typed.

2

I can’t give you a definitive answer but here is some additional information on the biomechanics of the QB throw and setup:

Improving throwing motion.

Proper Mechanics.

Step by Step Mechanics Breakdown.

“Best Throwing Video Ever” (their words not mine, but it’s pretty good).

Throwing Motion Mechanics.

Breakdown of Drew Brees’ motion (video).

3

You mean, the arm that doesn’t have the ball? My guess is that it’s so they can impart more momentum to the ball without falling over.

4

I played a little QB. The non-throwing arm and hand starts the rotation of the shoulders and back and adds to the angular momentum of the upper body so that the throwing arm rotates around faster and imparts more tangential velocity on the ball - much like cracking a whip.

5

In volleyball, the off arm also functions to make sure you are square to the target. I’d imagine that translates to football as well.

6

But a figure skater in a twirl with one arm out and one tucked would fall down, right?