What if aliens would have a possibility to capture human soldiers and interrogate them?
After successful interrogation the aliens could have your base location(s) and they would attack one or multiple base/bases!
Maybe they could stun your soldier at the battleground, and if would you lose that battle, aliens will take your unconscious soldier and interrogate him/her. Dunno if this has already been brought up, but I just thought I'd atleast propose it
PS. Oh sorry, this was supposed to be on the suggestions area. Maybe admins can move this to right forum section?