The strike zone varies from batter to batter. The width of the strike zone is the width of home plate. The height is from the batter's chest (usually the letters) down to the batter's knees. The strike zone doesn't necessarily go by how tall the batter is, but by how the batter's stance is in the batter's box while waiting for the pitch.
under your waist
Your strike zone in baseball is from your chest to your knees and the width of home plate.
the strike zone is wherever the umpire says
from the chest to the knees
Assuming you mean in baseball: The number of pitches in the strike zone versus the number of pitches outside the strike zone.
A ball in base ball is a ball outside of the strike zone. The strike zone is from mid-chest to knees and over home plate. Any ball inside the strike zone is a strike.
Traditionally, the strike zone extends from the waist to the letters of the team.
No - only a piece of it - doesn't even need to be 50% or more - as long as the umpire sees ANY part of it in the zone its a strike
The strike zone is a box that is the width of home plate, and the length of the space between the batter's chest and knees.
The With of the plate and from the hitters knees to his chest
Umpires do not decide or announce changes in the strike zone, that is determined by the MLB Rules Committee. The last such change by the committee was in 1996, when the lower limit of the strike zone was changed from the top of the knees to the bottom of the knees. Umpires simply call the strike zone on what THEY PERCEIVE as the size of the zone in the rules in effect at the time.
The "strike zone" is baseball is different with each player. It is determined thus: When a batter takes his natural stance at the plate, the "strike zone" is the area over home plate between the batter's arm pits and the top of his knees. Many umpires have their own determination of the "strike zone", but this is what it is suppose to be.