In both high school and college football, while a team is on offense it is required to have a minimum of five players wearing jerseys numbered 50-79 who line up on the line of scrimmage. These poor souls are branded “ineligible,” as in they are ineligible to receive a forward pass, regardless of where they actually line up. So you cannot throw number 63 the ball, even if he lined up in the backfield. Similarly, if 63 lines up at Flanker and 22 lines up as a covered guard, neither can go out for a forward pass, as 22 is barred under the traditional rule that only allows ends and backfield players to be eligible for forward passes. And unlike the NFL, High School and College ball does not have a reporting system to allow ineligible guys to become eligible again. This rule's animating rationale appears to have been an attempt to stamp out tackle eligible plays, possibly as a direct rebuke to Bear Bryant who in particular had used such plays with success.
This is the base rule. The A-11 offense seeks to liberate those five from their “ineligible” status by relying on an exception to the general rule: the “scrimmage kick” rule.
In both high school and college, if a team goes into a “scrimmage kick formation” (more on this in a bit) the offense can disregard the rule requiring the five-man minimum of 50-79 numbered players and can, if it likes, put eleven guys on the field who all have eligible numbers. (Still, only a total of six guys remain eligible to receive a forward pass: the two ends and the four backfield players. ) The scrimmage kick exception was put in sometime after the number-eligibility limitation to allow more flexibility on punt plays by allowing teams to put faster players on the field rather than having to keep five linemen on the field.
So the A-11 offense is built on this scrimmage kick exception. To confuse the defense, the offense puts as many guys up near (but not on the line) as possible, and then shortly before the snap six of them (two ends and four interior linemen, not counting the center who is already on the ball) move onto the line, set for one second, and the ball is snapped and off the offense goes. The defense then must figure out who is eligible to receive a forward pass. The offense compounds this confusion by having the ineligible guys put their hands up, run bubble plays or little dummy hitch routes behind the line. They also can of course block for run plays or for screens, and they can even receive laterals (backwards passes), but a lineman wearing number 63 could already do that without the scrimmage kick formation. Note also, however, that once a player has lined up on the line of scrimmage he remains ineligible and you can’t then shift who is on and who is off multiple times.
What is the scrimmage kick formation? I saved this for last because the formation is defined differently for college and high school. In high school, a team lines up in a “scrimmage kick formation” anytime they have a “receiver” of the snap lined up seven yards deep or more. (I say “a receiver” versus the receiver because it doesn’t have to be the actual recipient of the snap. For example, on a fake punt the punter lines up more than seven yards deep but the actual snap might go to the upback who is lined up only four yards deep.) So all a high school team needs to do is put its quarterback seven yards deep and then it may employ this scrimmage kick exception. This is how Piedmont turned the A-11 into an every down offense.