I had this situation come up in a game that I played;
LS declares objective and one attacker.
DS plays an event that has the one LS attacker discarded.
LS player wants to play Admiral Ackbar.
I believe Admiral Ackbar can be played, but I am unsure of when. The engagement hasn't come to the "Declare defenders" step. Can the LS player play Admiral Ackbar after defenders are declared or even after the last declared defender is focused to strike?