The first incantation of the ruby was a parlor trick created by a poor magician, Par, to simply have the ruby hover and impress some people enough earn a few stray coppers that people may throw. With the money and his concentration on bettering the small act he used his power to make the ruby able to smack thrown copper out of the air to better entice spectators to throw money at him.
He soon had the ruby enspelled well enough to block even the most deftly thrown copper. The young rich in the city quickly helped his fortune grow as it became a contest to see who could hit the street magician. Only one has known to be able to get through the rubies protection. (possible plot point)
Once balanced successfully on the blade it swirls around the wielder for 1-4 minutes protecting him/her from any attempt to hit with an inanimate object. Punches and kicks will not be blocked. Will block any human wielded weapon size. Large giant size weapons will hit the ruby like a baseball.
To balance the ruby on the flat of the blade takes good agility and concentration for the way the ruby is carved does not lend to it being easily balanced.