In basketball, a block (short for blocked shot) occurs when a defensive player legally deflects a shot from an offensive player. The defender must not touch the offensive player's hands or otherwise a foul is called. In order to be legal, the block must occur while the shot is traveling upward. If it is heading downward when the defender hits it, it is ruled as goaltending and counts as a made basket. A goaltend is also called if the block is made after the ball bounces on the backboard.

Largely due to their height and position near the basket, centers and power forwards tend to record the most blocks. A blocked shot is considered to be one of the most exciting plays in basketball. A player with the ability to block shots can be a great asset to a team's defense, as he or she can make it difficult for opposing players to shoot near the basket and gives opportunities for counterattacks such as fastbreaks.

To be a good shotblocker, a player needs great court sense and timing, and good height or jumping ability. A great shotblocker might not block every shot, but can intimidate opponents to alter their shots, resulting in a miss. Some of the best shotblockers in the NBA were/are Bill Russell, Wilt Chamberlain, Mark Eaton, Manute Bol, Hakeem Olajuwon, Dikembe Mutombo, Alonzo Mourning, Ben Wallace, Yao Ming and Andrei Kirilenko. Some slang terms for blocks are rejections, denials and swats.

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