F1 does not have to come to a stop (although, he may) if he attempts a pick-off.

If he is going to pitch he must come to a complete stop (entire body). He may not come to a complete stop (entire body) a second time. Once he begins his delivery he may "freeze his leg" provided some other part of his body continues to move.

Most times when an offensive coach complains about the "freeze", the pitcher, in reality still made movement of the glove or his head or his torso.

Right. When I balk this move, I never say anything about "continuous delivery," or whatever. He started and stopped. Balk. Doesn't matter where, if anywhere, he throws the ball.