Emerged further from the murk of 'this' and 'that' thanks to bind() and custom events.

Am using event listener on event "turn_over" to know when to change from Offense to Defense.
Call $(document).trigger("turn_over") at end of offense/defense turns.
Moved everything relating to setInterval/Ajax checks for opponents' shot on defense turn into Defense object.
Used bind() in making it possible to call setInterval internal to an instance.
Similarly for bind() in calling turn_over_listener internal to Game.