Was "friendly fire" more of a danger during times when warriors fought in one big group?

I’m watching King Arthur and the end scene with the big battles makes me wonder how, in the heat of battle with blood and smoke and stuff flying everywhere, can each side tell its own soldiers from those of the other side. Nowadays, battle is still pretty hectic but, from what I understand, because of the prevalence of long distance projectile weapons as opposed to swords, knives and the like each side sticks pretty well to its own side and there isn’t much of a big group melee.

So, I’m thinking killing an ally was a real danger what with all the flying swords and mass of violently moving bodies. Does anyone know if this was more common back in those days?