We need to read the BBW rule and the two paragraphs in the FAQ document that all go together.
What is a “crackback block”?
The crackback block is a block below the waist directed toward the line that runs lengthwise through the original position of the ball at the snap. This block is illegal unless the ball carrier is clearly beyond the neutral zone.
Is 10-2 block below the waist always legal?
No. Any block below the waist, including a 10-2 block, is illegal if it is:
- During a kick down—free kick or scrimmage kick.
- After a change of team possession.
- A crackback block.
- A peelback block.
Given the wording of the entire BBW rule, in addition to this FAQ document, and that a crackback block has to be by definition from "outside > in", in my opinion it's pretty clear that it doesn't apply to unrestricted players (player, ball, and block ALL within the tackle box).