The STRIKE ZONE is that area over home plate the upper limit of which is a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants, and the lower level is a line at the hollow beneath the kneecap. The Strike Zone shall be determined from the batter’s stance as the batter is prepared to swing at a pitched ball.

In running the last half of the distance from home base to
first base, while the ball is being fielded to first base, he
runs outside (to the right of ) the three-foot line, or inside
(to the left of ) the foul line, and in the umpire’s judgment
in so doing interferes with the fielder taking the throw at
first base, in which case the ball is dead; except that he
may run outside (to the right of ) the three-foot line or
inside (to the left of ) the foul line to avoid a fielder
attempting to field a batted ball;
Rule 5.09(a )(11) Comment (Rule 6.05(k ) Comment ): The
lines marking the three-foot lane are a part of that lane and a
batter-runner is required to have both feet within the three-foot
lane or on the lines marking the lane. The batter-runner is permitted
to exit the three-foot lane by means of a step, stride,
reach or slide in the immediate vicinity of first base for the sole
purpose of touching first base.