Key Points
The Strike Zone and Calling Balls and Strikes is one of the most fundamentally important parts of baseball and to many, the most important job an umpire has.
In all grades but particularly when starting out and in juniors it is important for the learning umpire to look for strikes.
Do not be concerned with the ball that "just missed" the zone. A ball that "just missed" possibly "just clipped" the strike zone as well and you will be more consistent, players will be happier, and the game will go smoother if you call those close pitches strikes.
It is important to remember that the strike zone is a three-dimensional object and is the entire area above home plate and is not just the “front edge” as you may see on TV.
For a pitch to become a strike it must pass over any part of the plate but must enter and leave the strike zone between the upper and lower limits.
What the Rule Book Says
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.
A STRIKE is a legal pitch when so called by the umpire, which:
(a) Is struck at by the batter and is missed;
(b) Is not struck at, if any part of the ball passes through any part of the strike zone;
(c) Is fouled by the batter when he has less than two strikes;
(d) Is bunted foul;
(e) Touches the batter as he strikes at it;
(f) Touches the batter in flight in the strike zone; or
(g) Becomes a foul tip.