Ralph,
About 90% of high school varisty games in the state of Arkansas are using 3 man mechanics. Therefore, there are 3 pairs of eyes on the court and at least one pair is watching "off-ball" play. A typical foul is an off ball foul for illegal contact when an offensive player attempts to set an off ball pick (screen) and slides (moves)laterally into the opposing player and most of the time with arms up and elbows out.
Read and understand Rule 4 Section 39 of the Rule Book and screening contact (10.6.3) in the Case Book.
Like the the block/charge call, the illegal screen call you mention is usually a bam-bam
play and can happen in a blink of an eye. The call is usually a block call (S7) or sometimes a push call (S10).
The most critical time for me is when I am moving down court with a fast break and B1 moves up behind A1 who has his/her back to B1 to catch a long pass. Time and distance are relevant. Be ready to make the right call. Good luck.
