The Rule is on pages 76 to 77:
My reading of this is that the turning BG can only do so if they are not eligible to fight as an overlap against the BG they are turning onto.SIDE EDGE TO SIDE EDGE CONTACT
... [opposing] Battle Groups in side edge to side edge contact are not committed to combat and are free to move away. If they do not move away, no combat occurs unless they are eligible to fight as an overlap. If not they can engage in Melee as follows:
A BG that is in side edge to side edge contact with an enemy BG can turn 90 degrees to face it ...
Am I wrong? If so, why?
Dave Allen


