Players must observe a number of simple, but critically important rules when bringing a Tactician card into play.
• A Tactician card must always be played when indicated. Some cards may be played out of turn, during the opponent’s game turn, or in reaction to one of his actions or card play.
• When playing a Tactician card, place it in front of you at the appropriate time (possibly in reaction to one of your opponent’s actions), and read it aloud.
A Cavalry unit with an attached LEADER, will combat with 1 additional die. Play this card when the melee combat is announced.
so I would say it must be played when melee is announced, and squaring is determined after that.
Morale of the story.. use Cavalry Leader card vs Artillery or Cavalry
Glory is fleeting, but obscurity is forever.
Yes, before. That is the way I play it too. There are a few unclear areas in the rules. I like to come to agreement with my opponent on these unclear areas before we start a game and write them down so we have a document going forward of rules interpretations.