In baseball, a stolen base is when a baserunner advances to the next base while the pitcher is throwing the ball to home plate. In baseball statistics, stolen bases are displayed as SB. It is possible to steal second base, third base, or home plate, but not to steal first base.
If the defense does not try to put the baserunner out (for example, if the catcher does not even look his way), the play is called defensive indifference (also called fielder's indifference). No stolen base is credited to the runner in this case. Defensive indifference is usually only scored instead of a stolen base when the game is in a late inning and the team with the stealing baserunner is down by more than one run. MLB Rule 10.07(g) defines defensive indifference.
A player who is good at stealing bases needs not just running speed, but also good base-running instincts, quickness, and split-second timing. The scoring and guidelines for awarding a stolen base to a runner are covered by rule 10.07 of the Major League Baseball rule book.
If a player is good at stealing bases, his manager may let him try to steal a base whenever he thinks he can. A player who is allowed to try to steal whenever he wants is said to have the "green light". Players who do not have the green light may only be allowed to steal when a coach or manager tells him to.