Delayed Steal
The runner waits a beat, then goes when the middle infielders relax.
How it actually works. The runner takes his secondary lead as normal, then breaks as the catcher is transferring the ball back to the pitcher. The bet is that neither middle infielder has moved toward second, because both of them read the pitch as over and looked away.
Why it is done, and when it is wrong. It is not a speed play, it is an attention play, and that is what makes it so useful against a good defense having a lazy inning. The tell that it is available is a middle infield that turns its back to the runner after every pitch. Against a team that stays alert it is a comically easy out, which is why it is a once-a-series play rather than a strategy.
At Little League and travel ball. It is close to unstoppable in youth ball and coaches should use it and also be honest about what it teaches. It works because twelve year olds stop paying attention, and the lesson for the defense is worth more than the base.
Batter's Eye: look up anything in baseball