Base-line seal/screen

[barknoll]

Can someone please explain any detail in what an official is looking for in calling a baseline screen/seal illegal

Against a zone defense, offensive player behind defender---posting up wide, if player holds position and allows wing to dribble drive underneath for layup----why / what would cause a call for illegal screen other than if referee would say moving feet or a hold?

Thanks in advance---any help appreciated

would it help for the offensive player to show a high target hand for potential pass as long as possible or to show the hands low as in looking for possible bounce pass???/

had the number 2 team in state do this several times against us early in season with no call----can't beat them--join em'