Combat Charge: Attack + 10, Defense - 25 (or 0)
Defense Formation: Attack - 20 (or 1), Defense + 15
Perhaps the benefits of some real formations including archers and
such could be incorporated. The idea here is to make the penalty
pretty steep but have a pretty good bonus. This way, people can use
them for special situations (such as charging a castle) but won't
use them all the time.
No, I haven't thought this all the way through so rip away!