Can the infantry unit play a First Strike card, and then Form Square? I think the answer is "no," and that you can either form a square OR play the First Strike card. But the rules don't specifically say that. It was my opponent's birthday today, so I let him get away with it. For today, anyway.
Bayernkini wrote: But if the Infantry is forced to retreat by the CAV attack, the INF may form square, if the CAV makes a Cavalry Breakthrough and battles again the INF (because this is a "new" battle).
It´s same with using 2 First Strikes: If a Cavalry battles first attack and makes a Breakthrough and battles a second attack, we have 2 own battles.
In each battle the Defender can decide new, if he play a First Strike OR form a Square!
So it´s possible, that the Defender plays 2 FS against the same (Cavalry) Attacker, one in Initial Attack, second in breakthroug Attack , but this is already in the FAQ.