How to outflank an enemy battle line
In DBMM putting some troops behind an enemy line while engaging it frontally is often a battle winner maneuver.
First of all, it makes much easier to kill enemy elements. Second, it diverts the enemy reserves from the use on the line of combat forcing the enemy to use pips that, in the case of clumsy troops, could be better used elsewhere. Last but not least, often the opponent reserves are not of top quality. This forces to expose elements that are easier to eliminate, as psiloi or LhF.
There are several ways to achieve this goal.
The easier one is by flank marching.
The flank march can be a double edge tool: a march late entering or never showing will backfire . This means that this maneuver should be well planned.
First of all the enemy must be kept near the march entering edge. An enemy advancing away from his deployment areas will gain several turns before the marchers will hit him, and this could be after he smashed the opponent army. The best way is to move first and block him in his deployment area. Being the defender or a mounted attacker is essential. Another way is to use terrain, like a river that is difficult to cross to the enemy troops but rough to their own. A small stream can trap enemy cavalry and pose no obstacle to friendly infantry. The downside is that a river placement is random, so there is always a risk factor in using it.
Second the enemy line must be pinned and should not be let maneuvered to face the flankers. Just the reserves, if any, could do that. This means that you should be aggressive.
Third the march should enter as soon as possible, so provide a -1 to the die roll is essential. A delay start stratagem is handy, as using a flank march with a brilliant general. Exposing your own army with an aggressive stance and with a portion missing is a spell for disaster. It is very important to plan that the contacting corps should have some sort of resilience to enemy to let it wait if needed the flank march showing.
Fourth, the marchers must be fast and able to engage successfully the enemy troops. They need speed to contact asap the opponent troops and menace flanks and rears, but if opponent has some reserve, they should be able to not be flushed away.
Another way is by manouver
Here is essential to be the first to move, again being the defender, using the mounted attacker die modifier or a night attack. The first turn will bring your troops on the enemy flank and deny him any march move, so what he usually does will be open his flank columns. Speed of execution is essential, as being aggressive and keep sending fast troops in open areas aiming to flanks and rear. Of course helps a lot facing an army with much less troops being able to deploy in the outer area.
Outflank by infiltration
It is made if you benefit by an huge terrain troops superiority and you have been able to set up some difficult going to use as approach avenue. The difficult going will also break the enemy formation creating several flank to be exploited. Having regular troops to avoid clumsy pip malus is very important, as being able to sally out of the terrain to attack enemy without risking quick kills. Reg AxS are the best troops, but also RBdF can fit the role if enemy has no or very few psiloi
Outflank by combat.
This is more difficult to do. It needs to mass on a side troops able to smash through the enemy line, followed by a small reserve of fast troops. As example, engage with CvO enemy LhO/F and once pierced through, use friendly LhF to deeply penetrate enemy rear areas.
Outflank by ambush
Another tactic that can work in a spectacular way is use an ambush to gain enemy rears. Ambush should be done by fast troops hiding in a sector that is far away from the combat lines. With medieval armies this is quite easy to achieve, being often fourth book armies quite small.
The trick is concentrate on a side and engage there the enemy, maybe refusing the corps that is more near the center while the attack is made on a side. The opponent often will bend his line to attack your flank that is in the center of the table, and the more he will wheel, the more he will expose the rear. If ambushing troops are far away on the opposite wing, they will have a lot of free room to march and roam in the enemies rear.
To add another consideration to what said above, it is essential to surprise the opponent or take him off balance by the speed of maneuvers / attack. Take and keep the initiative and let him dance to your music.
The more he will react to your plan the less he will be dangerous.