Secondary Lead
The extra shuffle steps a runner takes as the pitch is delivered.
How it actually works. The primary lead is what he takes standing still and it is limited by the pickoff. The secondary is taken after the pitcher commits, and it is timed so the runner's right foot lands as the ball reaches the plate, leaving him balanced and able to break either way.
Why it is done, and when it is wrong. This is the least glamorous and probably the most valuable baserunning skill there is, because it applies on every single pitch rather than on the handful where somebody steals. Two extra steps at the moment of contact is the difference between first to third and first to second, and first to third is one of the largest single swings in run expectancy available to an offense.
What people get wrong about it. A secondary lead that drifts, meaning the runner is still going when the catcher receives the ball, is a back pick waiting to happen. The shuffle has to end in balance.
At Little League and travel ball. Little League Majors rules effectively remove the primary lead, which makes the secondary the entire running game, and it is almost never taught. It is the fastest improvement available to a youth team's offense.
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