[swkansasref33]

if a lefty mirror-images the pick off, as if he goes to first then third, it is a balk, at least by all the rule sets i have used. MLB, NFHS, Legion, Babe Ruth, Cal Ripken. They all state that if a pitcher goes directly to first without stepping off it is a balk.

MLB Rule Book-
8.05 If there is a runner, or runners, it is a balk when—
(a) The pitcher, while touching his plate, makes any motion naturally associated with his pitch and fails to make such delivery;
Rule 8.05(a) Comment: If a lefthanded or righthanded pitcher swings his free foot past the back edge of the pitcher’s rubber, he is required to pitch to the batter except to throw to second base on a pick-off play.
(b) The pitcher, while touching his plate, feints a throw to first base and fails to complete the throw;
(c) The pitcher, while touching his plate, fails to step directly toward a base before throwing to that base;
Rule 8.05(c) Comment: Requires the pitcher, while touching his plate, to step directly toward a base before throwing to that base. If a pitcher turns or spins off of his free foot without actually stepping or if he turns his body and throws before stepping, it is a balk.
A pitcher is to step directly toward a base before throwing to that base but does not require him to throw (except to first base only) because he steps.

Have seen this happen a few times.. shocked the hell outta me the first time, and I almost didnt call it... based on the rule and comments I would call it a balk. He steps directly towards first without stepping off and he is required to throw.