This illustration is from the NCAA rule book. This is pretty much what I use in upper-level games with skilled pitchers- with the exception that the top of the ASA/high school strike zone is the armpits (for NCAA it's the sternum, maybe 1/2 a ball width lower than ASA/high school).
For a lower-level game, with less-skilled pitchers, about the only real adjustment I'll make is at the top of the zone. There, I will allow for the
bottom of the ball to nick the top line. I might give the pitchers
a little bit (1/2 a ball, or about 2 inches) around the entire perimeter of the zone.
Calling an acceptable zone is skill-level and age dependent. The strike zone described above for younger, less-skilled players works well for them. Try calling that same zone for an upper-level game and they will be ready to lynch you!
Calling a good strike zone is a balancing act. What you're trying to find is
the strike zone of least resistance- one that is acceptable to the participants for whatever level of ball you're working. You should be looking for strikes and giving the pitchers
a little benefit of the doubt. But you can't be ridiculous about it. Pitches at eye level, around the ankles or a foot outside should never be called strikes. These pitches are, essentially, unhittable and you would be doing the hitters a disservice to call those pitches strikes.
I find that if I use the above illustration as a starting point, then try to be as consistent as possible for both pitchers, throughout the entire game, that I get very few complaints about the strike zone. The strike zone itself is pretty darn big. Most pitches in the zone are so obvious that grandma sitting in the bleachers can see them. It's the
borderline pitches, at the fringes of the zone, where most of the controversy will occur. If you can establish some realistic visual boundaries, and consistently stick to them, it goes a long way toward keeping the controversy at a minimum.
