The scissors is an aerial dogfighting maneuver commonly used by military fighter pilots. It is primarily a defensive maneuver, used by an aircraft that is under attack. It consists of a series of short turns towards the attacking aircraft, slowing with each turn, in the hopes of forcing the attacker to overshoot. Performed properly, it can cause the attacking aircraft to move far enough in front to allow the defender to turn the tables and attack.
The scissors is a close-maneuvering technique, and as such, is really only useful when defending against guns or low-performance missiles. It was a major technique from World War I to the Korean War, but is much less common today. The introduction of high-angle missiles makes it much less effective, as the attacker can shoot even when the defender is not in front of them. Modern aircraft also make it difficult to use this technique as they maintain energy much better than earlier designs and the maneuvering limits are often the pilot's physical limitations, not the aircraft.
In fact, for many years now, fighter pilots flying aircraft with even a reasonable thrust-to-weight ratio and average wing loading are well-advised to avoid engaging in a scissors maneuver, since any turning, rolling, or slow-speed disadvantage the pilot's aircraft might have with respect to that of their opponent (or pilot skill in energy assessment and management techniques) will quickly become evident in the scissors, and lead to their defeat in short order.
Types
Basic fighter maneuvering theory recognizes two different types of scissors maneuvers; the flat scissors and the rolling scissors.
Flat scissors
A flat scissors maneuver typically results when two fighters of similar capability encounter each other at similar speeds and in the same plane of motion, and the attacking fighter has failed to press an initial positional and angular advantage into a kill, and has "overshot", or passed behind the defender. (To overshoot is to fly from an AOT (angle-off-tail: the angle between the nose of the attacker and an imaginary extended line from the nose through the tail of the defender and extending behind it into the air) of less than 90 degrees to an AOT of greater than 90 degrees.)
As such, an attacker who finds themselves in a flat scissors has transitioned from an offensive to a neutral engagement and has lost their offensive advantage. The defending pilot is often surprised initially by what was likely an unobserved attack from the rear, and while they have survived a highly defensive situation that has become a somewhat neutral encounter after the overshoot, the defender must still react quickly. After the overshoot, if the defender chooses to remain engaged with a nose-to-nose turn (that is, a turn toward the attacker in the general direction of the attacker's direction of flight) to either gain the advantage or maintain the neutral situation, the flat scissors is a common result.
Once initiated by the defender, it is difficult to disengage from a flat scissors without being exposed to danger from the weapons of the other aircraft. An experienced and patient defender might be able to turn the scissors to their advantage, however. The defender possessing superior turning capability may also initiate a flat scissors offensively, although this is certainly a dangerous gambit (as it involves allowing the attacker to approach to close range from behind), but one that may be forced upon the defender by the attacker's superior engine power or speed. After becoming aware of a more or less co-planar attack from their rear hemisphere, the defender uses co-planar energy techniques (using power reduction, uncoordinated flight, flaps, slats, or speed brakes) without moving out of the initial plane of the attack. By remaining in the same plane of the attack, the defender might be able initially to deceive the attacker about the two airplanes' rate of closure, quickly placing the attacker into a position in which a successful attack cannot be made due to close proximity, too much angle-off-tail, or both.
In any case, if both pilots' reaction to a co-planar overshoot with only a minor air-speed differential is a co-planar nose-to-nose turn, then a flat scissors will often result.
During the repeated brief nose-to-nose passes it is possible to get off what is called a "snap-shot" (a very brief high-aspect shot) at the opponent fighter. This process of 180-degree rolls and reversed turns can be repeated many times while each pilot seeks a positional advantage through energy management, and seeks to avoid a disadvantage.