The I formation is one of the most common offensive formations in American football. The I formation draws its name from the vertical alignment of quarterback, fullback, and running back, particularly when contrasted with the same players' alignments in the T formation.

A fullback (FB) is a position in the offensive backfield in gridiron football and is one of the two running back positions along with the halfback. Fullbacks are typically larger than halfbacks, and, in most offensive schemes, the fullback's duties are split among power running, pass catching, and blocking for both the quarterback and the other running back.