The main affect is a psychological attack that pressures your enemy and lowers their morale due to the feeling of being surrounded and thus making it difficult to defend both sides. By sandwiching an enemy unit between two allied units, the enemy unit's combat strength will effectively be halved as half the troops will defend one side and the other half the other side.
The larger the second unit is the greater effect the psychological effect is; as shown by Heki's use of the tactic with a small unit at Dakan Plains where it allowed Duke Hyou to re-gain the momentum of his charge against the Wei forces and the effect it had when his larger unit was able to turn the tide of the whole battle against the Zhao forces in the coalition war.
If an enemy unit is targeting a specific unit of yours a other of your unit then rides parallel to the enemy unit causing pressure of the possibility of being suddenly attacked on the sidelines. This can be done with on one side or two. The more men on the sidelines the more the more psychological effect it gives. The sideline units notoriety also plays a role.
- Weakens the enemy attack.
- Chance that enemy makes mistakes.
- Chance of enemy giving up or members fleeing.
- The sidelines units can be of different types as long they aren't infantry.
- Needs multiple units to set up for greater effect.
- The extend of the effect is unknown.