OK, so I think I understand this scenario, bear with me...
-If this is in fact a Retreat from Combat, then the centre Blue stand is immediately destroyed as per the rules for Blocked Retreats (see WM Compendium page 45.)
-The remaining Blue stands are now separated either side of the Red stand, but have not yet contacted it. Apply any hits scored this round against the remaining two Blue stands and remove further casualties as necessary.
-Asssuming there is at least one Blue stand left, conduct any Pursuit as per the rules on WM Compendium page 47. If both Blue stands are still alive at this point, they may both be Pursued. This may mean a further Retreat by the Blue unit as two separate stands.
-If, following any Pursuit, both Blue stands are still alive and still separated from each other, they would follow the rules for a unit in Irregular Formation (see WM Compendium page 20, paragraph 5.)
Should they in fact become free to move in their own turn, (for example if all enemy units have broken off from Pursuit) the Blue stands would move at Half Pace. It would be in Blue's interests to move them back into a Regular formation at this point.
Hope this makes sense.....
Dark Omen