There is very little historical documentation available today on the shuriken art. The primary reason is that it was a rather secretive art. The technique of using the shuriken itself involved deception and surprise, and the main schools that utilized such methods of battle were also heavily involved in deceptive and secretive activities. What documentation that may exist would be held by the individual schools in the form of scrolls, the contents of which would only be shown to trusted students of the particular school. Furthermore, the simplicity and utility of the weapon was probably not held in such high esteem as that of the kenjutsu arts, which used highly developed techniques to wield swords of great refinement and advancement in metal technology.
Added to this is the fact that the shuriken itself was a supplementary weapon to the sword and other weapons within the main martial art schools of the time, and hence probably did not gain much popularity, even among students who were initiated into the secrets of the schools they were member of. Nevertheless, it did hold some historical and practical value, as there are occasional mentions of the use of throwing blades in the literature showing them to be held in a positive regard.
Today, there are many and varied types of shuriken, which suggests that the development of the art was rather fragmented and insular among various schools and areas. According to Yasuyuki Otsuka Sensei, headmaster of Meifu Shinkage Ryu Shuriken-jutsu, there were no standardized or formalized set of rules governing manufacture and use of the shuriken blades as there were with the katana, or Japanese sword, and this would have aided in the proliferation of differing designs and schools around the country.
Chikatoshi Someya Sensei attempted to form some sort of categorization of shuriken in his book "Shuriken Giho", but admitted that without historical records, such categorization is purely speculative, and that there were a number of examples that could not fit in his categorization method as well. Nevertheless, such categorization can be useful today for the purpose of describing and discussing the art and the items in use.
The throwing star also known as a shuriken, it is probably the most popular weapon people relate to ninjutsu. The shuriken is an important ninja tool but is not meant to be a deadly weapon, instead it is mainly used to distract an opponent.
To distract an opponent it could be used to bridge the gap, for example if the ninja wanted to get close to his attacker he would throw a shuriken in the way someone might throw sand in some ones eyes to gain a split second to enable an attack, or maybe for an escape plan.
The shuriken was normally carried in concealed pouches of seven, they were tossed both under hand and over hand at short distances of about several meters. When throwing the shuriken the wrist is snapped into a straight line with the wrist and forearm.
Sometimes the shuriken would be held in the fist and the sharp edges would protrude through the knuckles enabling the ninja to scratch the opponent. Often the shuriken was left to go rusty so as to cause infection to the scratches.