From a reader: "What's the purpose of the 6-7 men on the line of scrimmage rule? What exactly is the rule? Often the linemen are lined up slightly off the ball, but they're considered on the LOS."
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The basis for the seven-man rule (it is always seven men on the line of scrimmage for the offense and field goal/PAT/punting units, in all circumstances, never six or eight men) is so ingrained in modern strategy that it's barely mentioned, even though it's at the heart of every system, formation and non-trick play devised for the last hundred years. A lot of fans probably don't understand what makes an "illegal formation" illegal, or why it's illegal to begin with.
Beware the killer wedge.
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Restricted by the rules, Yale's front line nervously held its position.
After amassing twenty yards at full velocity, the "flyers" fused at mid-field, forming a massive human arrow. Just then, Trafford pitched the ball back to his speedy halfback, Charlie Brewer. At that moment, one group of players executed a quarter turn, focusing the entire wedge toward Yale's right flank. Now both sides of the flying wedge pierced ahead at breakneck speed, attacking Yale's front line with great momentum. Brewer scampered behind the punishing wall, while Yale's brave defenders threw themselves into its dreadful path.
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This restriction more than any other is the main reason offensive philosophy is more cyclical than evolutionary, because the five-man interior line is a staple almost by definition - if you have to have five guys on the field who are not eligible for a pass and have to line up along the line of scrimmage, they may as well be the most giant monsters you can get your hands on to push the other team around - and there are only so many options with the rest of the guys on the field. That's why your standard formation for years has looked like this:
...it's just moving a couple of pieces on the board. It's worthless to try to stretch the ineligible linemen across the field when the only function available to them, by rule, is blocking. Because of the seven-man restriction, there is a very limited set of alignment possibilities among the five eligible receivers, which allows defenses to make some automatic assumptions and makes the eligible/ineligible distinction pretty easy to spot when those possibilities become familiar.
Those assumptions can be (though very rarely are) exploited. LSU, for example, took advantage of the quick calculations defenders make in their alignment in the BCS championship game, when they came out near the Ohio State goalline in a weird formation that looked something like this:
WR QB WR WR
It's the kind of thing that only works once, though.
As far as penalties, illegal formation flags are almost always the wide receiver's fault: officials announce the number of the last lineman on the line, but the receiver who didn't establish himself as the seventh man is the culprit. As far as linemen not lining up along the line, sometimes a tackle anxious to get into pass protection is hit with a flag if he's too far behind the line, but it's so common as passing increases that officials let it slide unless the guy's egregiously in the backfield. It's a judgment call, and frustratingly ticky-tack when whistled.
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