Basketball Defense Rules

In basketball, playing defense means trying to stop your opponent from scoring. The rules of basketball spell out how and under what circumstances the defense can attempt to stop offensive players. The majority of personal fouls are called over illegal contact by defenders. Understanding the basic rules of basketball defense can make you a better defender and all-around player.

The rules of basketball dictate what defenders can and can't do on the court. (Image: Kane Skennar/Photodisc/Getty Images)

Legal Guarding Position

Basketball rules define the exact movements and position a defender must take in order to establish legal guarding position. A player who has both feet on the ground and is facing his opponent has established legal guarding position, according to the National Collegiate Athletic Association. Any contact with an offensive player while a defensive player has legal guarding position is considered either incidental contact or a foul on the offense. A player may move to the right, left, or back up and still keep the same legal guarding position. Once a player has established legal guarding position, it is the responsibility of the offensive player to move or change directions in order to avoid contact.

Secondary Defender

In college and the National Basketball Association, a secondary defender is not allowed to draw an offensive foul while underneath the basket. A secondary defender is defined as a player on defense who is not actively defending a player making a move to the basket, but comes in to help a teammate acting as a primary defender on the offensive player. In the NBA, a semi-circle is painted under the basket to help officials determine if a player is positioned in an area where this rules applies. In college basketball, no line exists, and it is up to the official to determine if the secondary defender is under the basket.

Defensive Three-Second Rule

In the NBA, defensive players may not be in the free-throw lane for more than three seconds without being within arm's reach of an opponent. Defensive players may defend anyone on the other team in order to comply with this rule, including double-teaming another player. The count is suspended when the ball is in the air on a field-goal attempt, when the player begins actively guarding an opponent, or when there is a loss of team control by the offense. Failure to comply with this rule results in a technical foul. One free throw is awarded to the offensive team, and the ball is awarded out of bounds to the offensive team on the side of the court at the free-throw line extended.

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