What is considered an illegal screen in the NBA?

In the NBA, an illegal screen, also known as an illegal pick or moving screen, is defined by several key criteria:

Positioning and Movement

• An offensive player setting a screen must remain stationary and not move into the defender. If the screener moves toward or sideways into a defender to create contact, it is considered an illegal screen345.

Vertical Plane and Body Position

• The screener must keep their legs no wider than shoulder width apart and not extend their legs, elbows, forearms, or any other body parts outside the vertical plane of their body. This vertical plane is an imaginary cylinder around the player that they must stay within to avoid making illegal contact25.

Time and Distance

• The screener must give the defender enough time and/or distance to avoid the screen. This typically means providing at least one to two normal steps for the defender to go over or under the screen, depending on the defender's speed245.

Contact

• If the screener makes contact with the defender by extending any part of their body or fails to allow the defender sufficient space to avoid the screen, it is an illegal screen. The screener must allow the defender to avoid the screen without obstruction235.

Consequences

• When an illegal screen is called, it results in an offensive foul charged to the screener, and the opposing team gains possession of the ball via turnover234.

In summary, an illegal screen in the NBA occurs when the screener does not hold their position, extends body parts outside their vertical plane, or fails to provide adequate time and distance for the defender to avoid the screen.