also: pistol formation · pistol backfield
The quarterback about four yards deep with a back directly behind him. A compromise between under center and shotgun that keeps downhill running available.
The quarterback aligns a few yards behind the center, shorter than a full shotgun drop, and the running back lines up directly behind the quarterback rather than beside him.
The alignment keeps a direct snap while letting the back run downhill to either side without declaring a side before the snap. It can also ease the exchange for a young quarterback who is not comfortable under center.
pistol formationace, shotgun