Guarding the Post

[Rob1968]

This may be helpful:

2012-13 NFHS Rules Book POINTS OF EMPHASIS

4. Guidelines to enforce illegal contact. Escalating fight situations can often be traced back to illegal contact not being properly enforced and penalized.
a. Hand checking. Any tactic using hands or arms that allows a player on offense or defense to control the movement of an opposing player.
Examples of illegal contact are:
1) Both hands on an opposing player
2) Jabbing a hand or forearm on an opponent.
3) Continuous contact by a hand or forearm on an opponent.
b. Post play. Any tactic using hands, arms or body to control the movement of an opposing player.
Examples of illegal post play:
1) Hooking by the offensive player
2) Pushing, holding or slapping an opponent
3) Dislodging an opponent by using a leg or knee to the rear of an opponent
4) Dislodging an opponent by backing them down.

Please, note that a. 3) seems to define an armbar as illegal contact.
and that b.4) directly mentions "backing them (an opponent) down."

After all that, the judgement of the covering official comes into play, and may vary accordingly. . .sometimes you just have to officiate the game. . .