3rd to 1st Move Becomes a Balk

[Mrumpiresir]

8.05 If there is a runner, or runners, it is a balk when—

(c) The pitcher, while touching his plate, fails to step directly toward a base before throwing to that base;

Comment:
It is possible, with runners on first and third, for the pitcher to step toward third and not throw, merely to bluff the runner back to third; then seeing the
runner on first start for second, turn and step toward and throw to first base. This is legal. However, if, with runners on first and third, the pitcher, while in contact with the rubber, steps toward third and the immediately and in practically the same motion “wheels” and throws to first base, it is obviously an attempt to deceive the runner at first base, and in such a move it is practically impossible to step directly toward first base before the throw to first base, and such a move shall be called a balk. Of course, if the pitcher steps off the rubber and then makes such a move, it is not a balk.

I didn't think you would quote the entire rule or the comment.

RIF