Wow. My first robbing. I've been feeding a new package that I installed last week ... thought I'd been careful ... nothing spilled, top feeder (not an entrance feeder), reduced entrance so easier on the guard bees. And I was walking by that hive today on the way to the garden and bees everywhere, fighting. Balls of bees on the landing and tumbling to the ground, hive covered ... there was another small entrance where they could get in and out. What a mess.
I closed up the other entrance, stuck a bunch of grass in the small entrance (leaving just enough room for a bee at a time to get through) & watched it calm down slowly. It looks like things are back to normal now. But what a sight! Wish I'd had my camera with me.