Hidden ball trick
From BR Bullpen
The hidden ball trick is a play in which an infielder pretends to return the baseball to the pitcher, hides the ball in his glove, and tags out an unsuspecting baserunner when he takes his lead. The play is rarely attempted and rarely succeeds, so being caught is very embarassing to the victim. An important reason that the play rarely succeeds is that the pitcher will be penalized with a balk if he stands on or astride the pitcher's rubber without the ball. A runner who waits for the pitcher to take his position on the rubber before leading off will never be caught by the hidden ball trick.
Research has uncovered at least 250 instances of the hidden ball trick (though unfortunately the list is no longer available on the Retrosheet site).
Gene Michael became known as the master of the trick, having pulled it off five times in his big-league career.