The I formation in football is an offensive formation in which the quarterback stands behind the center and two other running backs stand in a line behind the quarterback. This an offense primed for running, but it can also feature a receiver split from the formation on either side of the ball and a single tight end. The I form can also see a number of other variations including double tight ends, slight shifts in the halfback's alignment, or even a three wide where the tight end is traded for a slot receiver. I formation hasn't been nearly as common in the NFL in recent years, but it still frequents college and high school playbooks.
The I formation is an old and common occurring formation, centered on powerful run plays. It's very much an in-your-face style offense with little misdirection. The halfback is the workhorse of this offense, his deeper alignment gives him the ability to identify weaknesses in the defense before the snap of the ball and then exploit them once he is handed the ball. The fullback plays a pivotal role in blocking for the halfback, often taking on stout linebackers to help the halfback get the extra yardage. This lead block will often happen on what's referred to as an iso, or isolation play. These plays focus on covering all defensive linemen and all but one linebacker. This final linebacker is the man the offense wants to "isolate," and it is the responsibility of the fullback to meet this defender in the hole. I formation also holds great utility in other short run plays such as traps, and even the occasional direct hand off to the fullback.
Because of its number of variations. The I formation can also prove a formidable formation for some short passing games. Simple slant or hitch plays can work excellently in this formation, especially when the defense has loaded the box to account for a run play. These pass plays add the necessary shift that forces a defense to respect the run, while never being able to overcommit in anticipation. This sets up especially well for play action runs.
The passing, though effective, is extremely limited. Long passes do not work well at all out of the I formation, and even short passes only work when the run game has been well established. The 52 defense serves well to mitigate the gains from the I formation. This holds true for all formations that put seven or eight men in the box at one time. The congestion makes it difficult for running backs to gain more than a yard or two per play, making first down conversion tough if not impossible. Over the I formation's main disadvantages come from its underscoring predictability and lack of varied play design and misdirection.