How did people know friend from foe in medieval (and later) battles?

I’d imagine most historical battles were pretty chaotic.

Eh, for a given definition. We can say that the usual depiction of two forces intermingled with each other as Hollywood often shows is Not It, however. I commend to your attention these following previous posts:

u/WARitter goes into the various means of identification combatants had then;
u/vonstroheims_monocle has a comparable glance on the matter;
but this, clearly the best answer, is one straight from His Majesty u/Henry_V_Rex.