Stealing a Base
Taking a base on the pitch.
How it actually works. It is decided in three places, and only one of them is the runner's speed. The pitcher's time from first movement to the ball reaching the mitt is the largest single factor, and the difference between a quick delivery and a slow one is more than the difference between a fast runner and an average one. The catcher's pop time, from the ball hitting his glove to it reaching the fielder's glove at second, is the second. The jump, meaning the runner's read of the pitcher's first unmistakable move, is the third.
Why it is done, and when it is wrong. The break-even point is what nobody quotes and everybody should. A stolen base gains you much less than a caught stealing costs you, because getting thrown out takes both the runner and an out at once. Roughly speaking a runner has to succeed around three times in four for the running game to be worth doing at all, which is why the modern game runs less often than the 1980s did and succeeds far more when it does. A team stealing eighty bases at a sixty percent rate is actively hurting itself and would have been praised for it forty years ago.
What people get wrong about it. Watch the pitcher's back heel and his front shoulder, not his head. Almost every pitcher has one move he cannot make to first base and one he cannot make to the plate, and finding it is what advance scouting is. Also watch the count: a runner going on a 3-2 pitch with two outs is not really stealing, because the batter swinging or walking covers him either way.
At Little League and travel ball. Stealing dominates youth baseball because throwing dominates youth baseball, and most of what looks like speed is a catcher who cannot make the throw. Little League Majors requires the runner to wait until the ball reaches the batter, which removes the jump entirely and makes it a pure footrace. Travel ball generally leads off, which is the biggest single adjustment a player makes moving over.
Batter's Eye: look up anything in baseball