The strong side of an offensive formation is the side of the field, left or right, where the offense has more blockers available for a running play.
Many defenses or defensive calls rely on designating the strong side of the offense and its opposite, the weak side. The defensive linemen may line up differently or slant to the strong side or the weak side, depending on the call. The linebackers, particularly the Sam linebacker and Will linebacker, are dependent on a designation of the strong and weak sides to line up. A player, usually the middle linebacker will often call out the strong side so the entire defense knows which side is strong. There is always a strong side.
Strong side is determined by following a set of rules. The first rule is that if there is a tight end to one side and not the other, the tight end side is the strong side.
If there are two tight ends or no tight ends, the side of the formation with more men is the strong side.
If the formation is completely balanced, the wide side of the field is the strong side.
Most formations are covered by the rules above, but there are some odd formations which cannot be easily categorized. Formations with two tight ends and a third off the line of scrimmage, for instance, can cause confusion. Because of that, it is important for the middle linebacker to call the formation, so all the defenders are on the same page.
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