[just another ref]

Apparently every detail needs to be covered.

Note the definition of a screen. .....legal action by a player who, without causing contact delays or prevents an opponent from reaching a desired position.

Note that intent is not a part of the definition. It is not uncommon for a player to use a teammate as a screen without it being a designed play, sometimes without the teammate even being aware of what is transpiring.

BUT, the other side of the definition is there as well. If the same player causes contact which prevents an opponent from reaching a desired position, it is an illegal screen, (foul) even if said player had no intention of setting/continuing a screen in the first place.