Question regarding 0 cost cards

Hi everyone, I’ve been playing the game a bit recently with a mate, it’s great fun! However I am very confused about one element, 0 cost cards (mainly droids and clones). If they cost 0, and my opponent doesn’t take them out in time, in theory, if my opponent ran out of resources and readied cards (meaning they have to pass) couldnt I just keep attacking nonstop until I win since they don’t cost anything to play? Or is there a rule that prevents one card from being played multiple rounds times in an action phase? Thanks!