Middle schools often play by rules specifically created for high school student-athletes because the book for high schools is the only one they have. To address this issue, it was decided to publish a book specifically written for middle schools.
 
Middle School Field Hockey Rules includes the full text of the Rules of Hockey and a list of modifications that take into account the special safety and skill level concerns regarding middle school student-athletes and the budgetary realities middle school athletic programs face that might otherwise restrict the growth of field hockey.
 
In short, it is less expensive to play field hockey games using Middle School Field Hockey Rules than those created for the complexities of varsity high school competitions. Price includes shipping to addresses in the continental USA. when ordered here. If you have Amazon Prime the book qualifies for free shipping and you can save a couple of dollars if you order from Amazon. 
https://www.amazon.com/Middle-School-Field-Hockey-Rules/dp/197440756X