A block in basketball is a successful deflection of an attempted shot by a defender. Defenders often play with their hands up or out, ready to stop any pass or shot attempts by an offensive player. Blocks can be made anywhere on the court, but are most commonly seen at the low post, closer to the basket. Block attempts are most often made by simply putting a hand up in the line of a player's shot or by swatting the ball in the air in its path toward the basket.
Players making blocks have to be careful to hit the ball and only the ball, because missing the ball and hitting an opponent or reaching in to interfere with an opponent's shot could result in a shooting foul and award the offense two free throws.
Some of the best shot blockers in NBA history include Dikembe Mutombo, Kareem Abdul-Jabbar and Tim Duncan.