At least you do that on siege, thats probably a bit easier to guess who's friend or foe. And on siege there's not many cav, if some at all.
On battle you may be able to notice who's on your side in the early time of the round by checking armor/banners and the same spawn. Later on you probably have some difficulties if you just see someone pass by.
"Attack or not".
But if you start hitting a friend and he does not react but probably report you, you won't notice it. ^^