Illegal screens are sometimes difficult, especially when the screen comes from behind the defender.

 

There are several key things to determine if a screen is an illegal screen.

 
Rule 4.40 Article 2 states that the screener may face any direction, time and distance ARE relevant, the screener must be stationary, except when both are moving in the same direction and path, and the screener must stay within their vertical plane (Rule of Verticality).

 

Here is another example of an illegal screen.  The screener was not stationary at the point of contact, and the screen is set outside the visual field of the defender.  In real time, it is hard to see this type of screen, especially when the defender does a great job of playing through the contact.  It is a judgement call.

 

In this case, the offensive team didn’t get a real advantage from the illegal screen.  It is the judgement of the official to make this call.  If it’s early in the game, do some preventative officiating and use your voice.  Tell the players to watch their screens.  Then, later if this type of screen is still happening, put a whistle on it.
 

 
Now, at the end of the video, the same screener sets another screen on the same player.  This time, I would not have judged this to be illegal.  The screen was set with enough time that the defender knew he was there.  The defender does another great job of playing through the screen.

 

If you missed the first post on Illegal Screens from Behind, click here.