Leading Off
Leaving the base before the pitch.
How it actually works. There is no leadoff and no pickoff game at Majors level and below. Stealing is legal, but it starts late, which turns it into a contest between the runner and the catcher rather than between the runner and the pitcher.
Why it is done, and when it is wrong. This is the biggest single difference between Little League and the game on television, and it is why the move up to a 60/90 field with leadoffs changes everything at once: pickoffs, balks, secondary leads and holding runners all arrive in the same season.
Batter's Eye: look up anything in baseball