Welcome to our third installment of the NBA Rule Authority. Throughout the 2011-12 season, we will be posting on this page explanations to some of the NBA’s more complicated rules to help fans better enjoy the game. This week’s topic is illegal screen violations.

A screen is an offensive blocking move where an offensive player without the ball “sets” a screen by standing near a defender in an effort to block his path, thereby freeing one of his teammates to drive or cut. A screen can be on-ball (when set for an offensive player with the ball to drive or shoot) or off-ball (when set for an offensive player without the ball to get open for a pass). To be a legal screen, an offensive player may not get into the path of a moving defender without giving him the opportunity to stop and/or change direction. The distance that needs to be given depends on the speed of the opponent.

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Below are four examples that will help you better understand what it is referees are looking for on these types of plays.

Play 1: Illegal screen in a pick’n roll situation. Screener rolls into defender.

Play 2: Illegal off ball screen. Screener moves into trailing defender.

Play 3: Illegal screen in a dribble handoff situation. Screener pivots into trailing defender.

Play 4: Illegal back screen. Screener does not give opponent one step.