Fireball & GA retaliation. (in General)

I'm just wondering if I am reading this right.

GA retaliates with a percentage of all damage inflicted on its targets by opposing Minions. GA damage is reduced by AC; GA damage type is the same as that for which GA is retaliating.

I had to change my strat, from FB mage to MM mage, because I was not only damaging my own team with fireball, my minions GA was hitting my mage for every time they took a hit from "friendly" fireball. Does fireball cause my mage to become a opposing minions? I was taking 5+hits from GA at times, 3 of which just coming from my own team.

sounds like you've figured most of it out, the Help section should have the rest...