I've always wondered how civilizations like the Mongolians and Scythians (who favored horse archery) prevented casualties during battle. I would have to imagine that their battles would be quite chaotic with so many mounted troops, and with all of those arrows flying around, were there any special tactics or methods used to The prevent these kinds of losses? Or Maybe these mounted battles were more organized and not as chaotic as I’d imagine them to be.
If there were a significant number of self-inflicted casualties in battle, are there any historical accounts of a situation in which "friendly fire" dictated the result of a battle?
With the Mongolian archers in particular there are a couple of different reasons, but the two main reasons are technological and equestrian.
The recurve bow is the first, the strength of the recurve cannot be underestimated. The second curve on each side of the bow allowed the archer to increase tension on the bowstring, adding more force and speed to the arrow without sacrificing mobility. Prior to the recurve the only way to increase tension, and thus force and speed, was to lengthen the bow. For example the English long bow fired a slower but heavier arrow on an arcing trajectory. The force created by the drawlength increased distance but required the static platform of an infantry archer to effectively fire. Both weapons required years of training to become effective tools, but the smaller size of the recurve allowed it to be drawn and fired from a mobile platform with formidable accuracy. The tactical benefit to the English longbow is penetration, the heavier arrow combined with the long arcing trajectory meant it could pierce heavier armor, but also made it an inaccurate weapon that relied more on weight of numbers. The recurve allows for increased force and speed, meaning lighter arrows, fired more rapidly, and more accurately, even from a moving platform.
The second is the Mongolian pony. The ponies the mongols rode were small, and fast. The size and relative strength of the Mongolian ponies meant that, while the Rocky terrain of Mongolia made them nimble, they couldn't hold the weight of equipment of a heavily armoured combatant. The issue of terrain, and a nomadic population made infantry ineffective in Mongolia. The nature of clan fueds required fast moving units who could strike quickly, accurately, and be gone before retaliation, or another clan could intervene. This type of combat requires lightly armoured flexible units. The recurve bow increased accuracy and power, the pony increased speed and maneuverability. The ponies gave Mongolians a firing platform that was more agile and faster than opponents, and the recurve was compact and accurate. These advantages allowed them to out flank slower better armoured units and kept friendly fire low by allowing them to isolate and overwhelm their opponents.
Basically, the Mongolians generally hit what they aimed at, and were fast enough to stay out of each other's way.