How often was accidental "friendly fire" in battles that were fought in close quarters with swords?

by unicycle_inc
darthturtle3

Hello! Not to discourage any more answers, but this question has been asked before, and OP might find this discussion interesting:
http://www.reddit.com/r/AskHistorians/comments/12wbn0/was_friendly_fire_common_in_pregunpowder_melee/