A couple of quoutes...
I have marked crack back or crack back block with << >>
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[..]
The commitee also approved changes regarding blocking below the waist by offensive players set wide in a formation or in motion. Previously, offensive players positioned more than seven yards in any direction from the middle offensive lineman at the snap, or in motion toward the ball at the snap, were prohibited from blocking below the waist toward the original position of the ball, commonly referred to as a <
>, behind the neutral zone and within five yards beyond the neutral zone.
[..]
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http://football.refs.org/rules/NCAA2000pr.html
This is from a newbye fan football site
I have quoted it because it describes the kind of play I tried to describe, My SAM Lb being blocked by Z receiver on a Pro Set Right Sweep Right play.
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Pitch and Sweep
DESCRIPTION
Sweeps and pitch plays are run plays to the outside. The major difference between the two is that the quarterback hands off the ball on a sweep where as the quarterback must toss the ball on a pitch. A major advantage of a sweep is that it allows a ball carrier to search for an open hole and can turn the ball upfield very easily. A pitch allows the ball carrier to get outside much faster and the play develops much quicker.
BLOCKING SCHEME
The basic blocking scheme for the offensive line is straight ahead blocking. The fullback can serve as the lead blocker or can be used to fake the counter play. A "sweep trap" can easily be incorporated - the blocking becomes similar to an outside trap, except the pulling lineman also sweeps to the outside to become the lead blocker.
Preventing an outside linebacker from maintaining outside containment can be useful to help get the back into the open field. This can be accomplished with the use of a <<"crack back">>. A crack back is where the X or Z receiver crashes down on the defender, resulting in a "blind side" block. The receiver can be in motion or can crash from their inital position. In other situations, the Y receiver can block down to create a double team at the outside corner. [..]
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http://www.football.com/playbook/ptchswp.shtml
Is it therefore, because A81 was further away than 7 yards from center, and running towards ball inicial position, an ilegal -below waist- block?
First I though all crack back blocks where ilegal, but know I think only those below waist.