Our middle school leagues, past and present have some form of this rule.
The old league:
* Man to man was required all game
* Double teaming is allowed in the paint.
* Players can switch or play help & recover d.
* Repeated violations are supposed to be two shots and the ball (most officials never wanted to call this though after the first warning
)
The new league:
* 5 periods (3 first half periods of 4:00; 2 second half periods of 6:00). This is to guarantee everyone playing time, though that can also be done with 4 quarter, IMO.
* Man to Man is required in the first half. Switching & help and recorver d is permitted, but trapping seems to be completely forbidden in the first half . Zone is legal in the second half.
* Nothing specified as to what to do for repeated violations.
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There is one coach in this league who feels playing a saggy 2-3 zone inside the 3 point line passes as man defense. We also have another coach who thinks having her player under the basket when ours is at the 3 point line is also man defense. Aside form them, though, eveyone seems to follow the rules as best as can be.
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Funny thing, too. CYO has rules regarding pressing and when pressure defenses can be used. I always keep my copy of the CYO rules at the table, knowing some officials probably have no idea what the rules are and would appreciate having something to refer to. At our opener this year, I had an official tell me to throw those rules in the garbage when I let him know what the league rules were.
I did have to chuckle to myself when he later admitted he didn't know our CYO changed a pressing rule 2 years ago. (That's why one doesn't throw the league-specific rules in the garbage
)