Here is something I heard about that may or may not apply. I think it was the picts that stripped down and went into battle naked. Not only is this intimidating ( wink wink ) but in case one was wounded there was no material to become lodged in the wounds, thus causing infection. Now! I have heard that early on the Scots would strip out of their great kilts and go into battle with just their shirts tied up between their legs. Not sure if this is accurate or not but the tradition may have distilled from those reasons.