A so-called “Hammer” is a shooting technique where the shooter delivers two quick shots to the center of mass of a target.
To do it, the handgunner presents the pistol, aligns the sights on the target, then breaks a shot, resets the trigger and delivers a second shot. There is no aligning of the sights before the second shot, but it must be followed by the correct re-aligning of sights and reseting the trigger, which follows the delivery of any shot.
At close range and from a proper Weaver stance, the two shots will strike close to one another. If they are within an inch of one another, you are probably shooting too slow- speed up. Once you can deliver two shots about two to three inches apart at three yards, it's time to move back to five yards.
Master the five yard line and move to seven, etc. A mild spread of as much as four to five inches is acceptable, as long as they strike within a few tenths of a second.
It is well established that a pair delivered in this fashion have a greater traumatic effect on a real-world opponent than two through the same hole over a greater span of time.