You'll hear about it from the first time 49ers quarterback Colin Kaepernick stands behind center, and listen to it be endlessly dissected in the Super Bowl.
    But just what is this pistol offense San Francisco is running?
    Put simply, it's a variation of the shotgun, a formation that has been in the NFL for decades. Former Nevada coach Chris Ault invented it, and gave it the name because it reminded him of a shorter version of the shotgun.
    In the pistol, the quarterback lines up 4-5 yards behind the center. Unlike the shotgun, the running backs line up behind the quarterback instead of next to him so they can be in motion when they get the ball and run north and south more easily.
    The tweak that makes the pistol even more effective, though, is the read-option. This what Kaepernick runs so well, and what Baltimore has spent two weeks preparing to stop.
    In the read-option, Kaepernick turns to his right and tucks the ball in the belly of his running back — all while keeping his eyes on the defense. Based on the first move the defensive end makes — either to the outside or toward the quarterback — Kaepernick will either leave the ball with the running back or pull it out and take off himself to the outside.
    Defensive players say the move causes problems because it forces them to hesitate a split-second to see what Kaepernick does with the ball. Often, that is just enough time for running back Frank Gore to slash up the middle or for Kaepernick to take the ball around the right end down the field for a big gain.