An Illegal Screen occurs when a player on the team possessing the ball attempts to Set a Screen on a player on the opposing team in a manner which is illegal and provides an advantage to their team.
A Screen can be defined as illegal when:
- The player Setting the Screen is moving their feet at the time when contact occurs
- The player Setting the Screen has their feet further than shoulder width apart
- The player Setting the Screen does not extend the hips, arms, elbows or knees outside their cylinder
- The player Setting the Screen sets the screen in a position that gives the defender adequate time to avoid contact with the screen
In the event of an Illegal Screen, a Personal Foul is assessed to the player who committed the Illegal Screen, and under NBA rules, no Team Foul is assessed (though under FIBA rules a Team Foul is assessed, however even if the Team of the player who committed the Illegal Screen is over their Team Foul Limit, no Free Throws will be awarded). Possession is then awarded to the opposing team of the player who committed the Illegal Screen, and they will inbound the ball from the sideline.