The Youth Rules and Best Practices Guidebook for Girls offers a comprehensive explanation of the rules and the rationale behind them. Each rule is broken down by age group. You can download the entire book for free.
Below is a table that lists which leagues are following the 3-pass rule and which are not. Also, please note that the count resets at a change of possession. The official has the only call on this ruling.
U13 MBGLL Select
U15 MBGLL Select
No player may shoot until her team has attempted or completed three passes (Minor Foul)
1. Keeper clear is counted as 1 pass. If the ball is played back to keeper, pass count stays at 1.
2. Pass or attempt is counted when receiver gains control of ball (not when passer throws it).
3. If a team loses ball to the opposing team (opposing team gains control of ball), pass count automatically resets to 0.
4. If keeper makes save and retains control of ball, pass count resets to zero. Even if attacking team intercepts keeper clear, they must make 3 more passes before shooting.
5. If keeper makes save but does not retain control of ball (rebound is outside goal circle), attacking team can pick up ball and immediately shoot because they retain accumulated pass count.
6. Umpires (not coaches) are responsible for audibly counting pass completions. Umpires should avoid saying, "you may shoot" / "go to goal." They should say, "you have 3 passes."