Punching your own squadmates, why?

This phenomenon went from rare to ubiquitous in the past couple weeks. Can someone explain why your own squaddies sometimes turn around and use melee on you? I've had it happen where I have climbed up high somewhere and am looking through a scope and they punch me off the cliff, and I end up getting shot first. Or I am looting a death box and I get punched away from it, which breaks the connection and I have to hold X again. I've seen two players go round and round punching each other, so maybe they are chatting and are game friends, but this has happened when the whole squad is running along and when a player overlaps they melee you. 

To be clear: we are not fighting over loot, and they are not looking for me to use an ultimate or to bring out the DOC healing drone. It's random. I just don't get it. Sometimes they are new players with just a handful of kills, so it's not like I'm holding back some pro players. I find it really annoying.

I had it happen in a game where one of the squaddies kept punching me for no reason, and then when we engaged another squad, I was the only one left standing. So I stood over his fallen body and jumped up and down until s/he turned into a death box, and then s/he quit.

I would actually enjoy it if your own squad could be damaged by your actions: melees, grenades, bullets. The game would play a lot differently if friendly fire was on. It's weird because you can accidentally kill your own team by calling in an airstrike (or even kill yourself! I was able to finish a daily goal by accidentally killing myself as Gibraltar, and then I taunted myself. Classic.) but you can lob a dozen grenades in their general vicinity if they are in close combat and it does no damage. 

Maybe there could be a limited time mode with friendly fire, or as you climb the ranked ladders it suddenly becomes active.