The strike zone.

[Brother Brian]

What exactly is the major league strike zone? Growing up, I was taught it was the letters to the knees, over the plate.

But to major league umps, it's anything from ankles to belt buckles on the left side of the plate, to "Oh, anywhere over the dirt is fine."

And it directly effects games. Pitcher's are effictively asked to hit moving targets.

[Dr. Mercury]

That's a complicated question. Since 2001, MLB has directed umps to call according to the rulebook (numbers to knees). In practice, it's according to the ump's interpretation--which is dependent on their positioning and the resulting sightline. As protective gear has become less cumbersome, umps have tended to crouch lower and this affects their field of vision.

So, yes, in some cases the umpires are blind. :D