Current rules I can figure out -- it's always the transition to Legacy that stumps me on occasion. Oh well, at least it's job security for Zen.
Forced March Battle: Straighten (if necessary) and move into this battle one of your units that has already engaged in a battle this turn in another Province. Forced March bows this unit after the resolution phase of this battle. This unit may not straighten in your next straighten phase.
SECOND-BATTLE RULE Before a unit that was in an attacking army at any point during a battle’s resolution moves to a battlefield during the same Attack Phase, the unit’s movement does not happen. Unlike the Rules of Presence and Location, the Second-Battle Rule does not restrict the taking of actions, but prevents movement as a cost or effect under certain conditions.
Now it is my understanding that several cards in existence allow a player to move a unit to a Province even if they have already been in a battle resolution that same Attack Phase, but I wanted to get clarification on Forced March. The card states a unit "that has already engaged in a battle this turn". Could that also be read as "that has already been in a battle during its resolution"? I ask because newer cards have specifically been referring to the Engagement portion of a Battle...