[Mike Simonds]

What rules do you follow in your league?

We follow National Federation rules in our high school league.

The National Federation rule book does not make reference to crack back blocks but in rule 2 it does define what a legal block is.

I don't have my rule book available but a legal block is contacting an opponent in a manner which is not a prohibited action such as clipping, holding, illegal block in the back, pass interference, personal foul, etc. The block must be made within the opponent's frame: at or below the shoulders, above the waist, at the front or side. Note that in the FBZ you can block your opponent below the waist but both players must meet the requirements I specified in my previous reply.

So to answer your question, lets say A82 blocks B53 as described in your example except the contact occurs at the side above the waist. This would be a legal block although I'm sure A82 won't like it.

Hope this helps you better understand the blocking rules.