[DownTownTonyBrown]

For NFHS...

Per RULE 3-3-1h
A coach, player, substitute, attendant or other bench personnel shall not:
h. enter the area behind the catcher while the opposing pitcher and catcher are in their positions;

PENALTY The umpire shall eject the offender from the game, unless the offense is judged to be of a minor nature. The umpire may warn the offender and then eject him if he repeats th eoffense. ... For coaches who violate g, h, i, j, k, or l, the umpire may (1) restrict the offender to the bench/dugout for the remainder of the game or (2) eject the offender. Any coach restricted to the bench shall be ejected for further misconduct.

A coach going behind the backstop to "checkout your strike zone" is not a "minor" offense.

I'm unable to find such a rule anywhere but in NFHS rules. So in OBR games, like for a 12 and under league where the coaches are mostly unknowing and there is no specific rule, perhaps one could consider it a minor error and restrict him to the dugout. In High School games, I feel this is grounds for immediate ejection.

OBR has a couple rules that are close but not specific:

3.17 Players and substitues of both teams shall confine themselves to the team's benches, unless actually participating in the play or preparing to enter the game, or coaching at first or third base. PENALTY: For violation the umpire may, after warning, remove the offender from the field.

4.05 talks about base coaches and them staying in their coaching box and removal from the game for violation... but it doesn't really address going behind the backstop.

Perhaps someone else knows of an OBR reference prohibiting such activities...??

But without a specific rule, perhaps a league rule, I guess in OBR games (non-High School), the offender is warned and subsequently ejected per 3.17?