Dawger...
"A lag roll or lag displacement roll is a barrel roll flown to get from lead pursuit to lag pursuit."
A lag displacement roll is flown to manage closure rate and to maintain or establish proper AOT, it is actually an excellent way to refuse a scissor engagement. A scissor is a defensive move and a lag roll is an offensive one. As TC stated there does come a point where the defender (scissor initiator) can convert to an offensive posture. This potential opportunity is entirely dependent on what the original aggressor does and if an overshoot (or potential overshoot) is created.
As agent said somewhere above its not getting slower per se its flying the farthest possible distance with the least forward movement, this invariably involves 3 dimensional geometry and maintaining very extreme AoA. This could be very accurately be described as a battle of lag rolls as both pilots attempt to establish AOT.
At its best the "scissors duel" is a tremendous test of spatial awareness, 3D tactics and plane handling skill. IMO at the level here the reality is more simple...
1) offer
2) engage flat
3) covert to rolling scissors
4) squeeze the con out front
1) scissors can only be offered not forced
2) once offered the initial move works best if its flat IMO, if the defender refuses and takes the high ground then the flat opener is more survivable for an average pilot then trying to force a rolling scissor. A lot of time the aggressor rolls back into the flat turn after smartly avoiding...actually with more E and a worse angle...
3) once you get the bite you need to convert asap to a more offensive rolling scissors. If the con is allowed to manage closure then the scissor will fail. A lot of players "scissor" with no purpose...like agent I view the scissors as an attack not a defense.
4) once your in a rolling scissor the real concept to work on is the amplitude of the components, learning to keep some speed by forcing the plane to the extremes of its flight envelope will allow you to fly farther "slower" while being faster then a pilot less comfortable with the edge of his planes envelope. Surprisingly to many newer playes you can win the scissor from a +E state vs a "lesser" pilot...
Again with this "lag roll is an offensive move". Everything is offense AND defense simultaneously. "I'm on defense so I can't lag roll" is a silly idea.
Guns defense comes in three parts. The initial break, the maneuver to defeat the shot, and the follow on BFM. When you perform a defensive break you are creating a decision tree based upon the actions of the bandit. The entire idea of the defensive break is to create the most Angle Off possible before the bandit reaches guns range. This doesn't mean a violent or abrupt break. In fact the most effective break smoothly builds the G to effectively disguise the high Angle Off and high G situation you want to develop. A good break turn will bring the bandit to the lift vector or slightly forward of it at the moment he reaches guns range. Stage one of guns defense is over and you have reached your decision point.
At this point in time you must evaluate the bandit and decide which follow on BFM is going to be most appropriate, execute a maneuver to spoil the shot and then transition into your chosen BFM and continue to evaluate.
If, when you get the bandit to the lift vector, you see he is pulling for lead and rapidly closing (you see him nose on or maybe even some belly side) then you are in an excellent position to initiate a nose high lag roll. Rolling the wings level and pulling the nose above the horizon will be enough out of plane maneuver to spoil his shot and if your evaluation was correct you will see his tracers behind your tail followed very shortly by the bandit crossing your 6. Continuing to roll towards the bandit begins the execution of your follow on BFM, The Lag Displacement Roll. All of this happens very rapidly.
Here is a Film demonstrating this.
Break turn to nose high Lag Roll Demo FilmIf you slightly misjudged the enemy closure and/or angle off or he recognizes the nose high lag roll early you will very likely end up in a canopy to canopy rolling scissors.
Lag Roll into rolling scissorsIf you misjudge badly the bandit will be right behind you and you will be very close to dead. I can't find a film of me doing that.
If, when you get the bandit to the lift vector, you see he is in lag pursuit and closure is small (you see the top of his aircraft) then the last thing you want to do is go nose high. If the bandit has killed all closure in a rapid deceleration you may be able to stay out of guns range by slightly relaxing G and continuing a nose low energy sustaining turn. More likely you will be forced into a maneuver to avoid the gun shot and a follow maneuver to force an overshoot. You don't want to do anything nose high for obvious reasons (If it isn't obvious then it will be once you try it a few times). If you have altitude and a desire to disengage a split S is an excellent choice to sling the bandit out. Doing this is simple. When the bandit reaches his guns firing point roll inverted and pull. This should spoil his guns shot and sling him outside your turn if you don't telegraph what you are doing and coax him into a guns shot.
If you don't have altitude for a split S or want to convert to the offensive nose low is still the way to go. A nose low lag roll after defeating his guns with a roll inverted is a good choice if you have some altitude to play with and get an overshoot from his guns shot. It can develop into a descending rolling scissors or quick offensive position depending on the skill of the bandit and your own execution.
If your break turn is poor or the bandit is fully committed to rapid deceleration and staying in the saddle AND you are on the deck, then you are getting into flat scissors territory. The break turn results in the bandit in lag pursuit firmly in your rear quarter and you have no altitude for a split S or nose low lag roll. Your only remaining choice is to try to force an overshoot using a flat scissors. A reversal to the nose low side is always better but most folks find this very difficult to perform. When the bandit reaches guns range and you have got him as close to the lift vector as he is gonna get (those two HAVE to happen simultaneously in every defensive break turn) then you must reverse the turn to initiate the flat scissors. Unload the airplane (Zero G...not negative G) and max roll rate technique, preferably to the nose low side while closing the throttle and kicking out any drag devices you might have (Flaps, speed brakes). Once you near a roll of 180 degrees watch the bandit. The instant you perceive he is rolling to match your reversal, unload the airplane and max roll rate technique to reverse again. By this time you should HAVE to bring the throttle up to keep flying. You should be on the ragged edge of a stall fighting to keep the airplane from stalling. If you initiate the third reversal and haven't kicked the bandit ahead of your 3-9 line chances are you never will. Once you get him out in front of the 3-9 line you will probably have to keep the scissors going to keep him there for about two more reversals. Don't be tempted to relax your technique for a snapshot. The instant you relax the scissors technique for a snapshot the bandit will scoot back into your rear hemisphere. (feel free to pull the trigger while performing your best scissors, just make sure you are still max performing the airplane while shooting)
That is about the limit of the decision tree created by a defensive break turn.
Break Turn, evaluate the bandit at the crucial moment, and then choose a follow on maneuver (Lag roll nose high or low, Split S, or a flat scissors) The events that follow that three step process may result in a rolling scissors or defensive spiral. A descending rolling scissors will degrade into a flat scissors eventually. All rolling scissors in prop airplanes will degrade into descending rolling scissors.
Again, I think much of the issue is a confusion of terms. Mainly because we don't take a building block approach to learning ACM.
There are two maneuvers. Rolls and pulls. That is it. EVERYTHING else is a combination of those two maneuvers. (Well, I will allow the unloading to zero G is technically a PUSH)
A loop is a 360 degree pull. A split S is a 180 degree roll followed by a 180 degree pull.
maneuvers done without reference to another aircraft are primary maneuvers.
When you perform a maneuver with reference to a target aircraft it becomes a Basic Fighter Maneuver. A split S performed in order to attack a low bandit is a BFM. Same maneuver as a split S just done for fun.
A barrel roll is simultaneous rolling and pulling maneuver. When you perform a barrel roll in order to continuously place the lift vector on (or slightly behind) the target (until angle off the tail decreases sufficiently) you are performing a lag displacement roll. Two aircraft engaged in simultaneous lag rolls against each other are in a rolling scissors.
A high yo yo is a simple nose high pull and a roll then another pull. What makes it an effective BFM is knowing that you pull the nose high to kill the closure then roll the lift vector to a point in front of the bandit and then pull again. If the bandit reverses in the middle of the yo yo it immediately creates a lag roll as shown in the following film
Yo Yo to Lag Roll Demo Film