Rule 2.00 CATCHER'S BOX

CATCHER’S BOX

The CATCHER’S BOX is that area within which the catcher shall stand until the pitcher delivers the ball.

DISCUSSION:

During an intentional walk, the catcher must remain within the catcher's box until the pitcher begins his preliminary motion to pitch. [BRD]

During a pitch-out, the catcher may leave his position at any time to catch a pitch or to make a play (see Rule 4.03(a)). [BRD]

Pitch out to nail runner stealing.
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Unless there is an intentional walk, the catcher is not confined to the catcher's box. The catcher must be directly back of the plate (see Rule 4.03: "When the ball is put in play at the start of, or during a game, all fielders other than the catcher shall be on fair territory.  (a) The catcher shall station himself directly back of the plate.").
Catcher leaves catcher's box for a pitch out, but the ball is pitched over the plate. Strike three.
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RULES REFERENCES:

Rule 1.04

Rule 4.03(a)

Rule 6.02(d)(1)(viii)

Rule 8.05(l)