you've already took all my swapsAhah, I've played you a few times Andy, also lost one time
Anyway, system will pick a random sticker from your doubles stash... Then you choose either attack or defense and system will pick a random user (without him knowing) and one of his doubles (I think so or maybe it's just a random sticker from all set).
Actually, these battles are very entertaining, there's no guarantee if you win, even if you have Ronaldo... For example, I've lost Ronaldo to Skriniar, even though Skriniar is way worse But Skriniar played defense and my Ronaldo defense sucks, while Skriniar attack sucks a bit less.
The better stickers are those who are both great in attack and defense, of course... That's why Beto won a lot with Kroos, he's a machine in both sides... But Kroos is not unbeatable, because let's say if Kroos plays attack and faces Ronaldo attacking too, he'll lose... Same if he faces Buffon defending.
Well, I'm out of doubles, though I can buy a lot more (Still have thousands of coins from previous virtual albums)... I'll play later some more