An unbalanced line is a feature of an offensive formation in which more than three offensive linemen line up on one side of the center.
An unbalanced line is not simply a formation where different numbers of players are only either side of the line. It is quite common for there to be a tight end on one side of the ball and not the other, but that is not unbalanced. An unbalanced line has to have more than a guard, tackle and end, which is why it needs four lineman.
The goal of the unbalanced line is to force the defense to line up in a way it is not comfortable or to take advantage of the blocking advantage if the defense doesn’t adjust. The proper adjustment varies from defense to defense, but it is usually to treat the middle lineman (who is probably the guard) as the center. If the defense does that, then everyone will shift toward the unbalanced side.
It’s not common in many offenses and isn’t run too often with the notable exception of short yardage situations and a few offenses who regularly employ it, like Stanford.
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