The reason I visited this shrine is that along with Morooka Kumano Jinja it is said to be one of the two football-related "power spots" in Kanto. On opening the shrine’s home page the first words you see are スポーツ振興の神, “The God of Sports Promotion.’

It was founded in 665 by Fujiwara Kamatari who was on his way to Eastern Japan by sea when his ship pulled into ‘Turtle Island (the Kame 亀 in the shrine’s name means turtle). He enshrined a sword there, invoked a spirit from Katori Jingu located in what is now Chiba, and prayed for safe onward travel.

Shortly before the Battle of Kojima (Shimosa Province) in 940, when Fujiwara Hidesato and Taira Sadamori defeated Taira Masakado at the Battle of Kojima in Shimosa Province , thus putting  an end to the     , the former had visited the shrine to pray for victory in the battle. After his victory he again visited the shrine and dedicated a bow and arrow to the shrine, naming them Kachiya (Victory Arrow) out of gratitude for the divine favour. In time, this led to the shrine being venerated by emperors and military commanders, including famous figures such as Minamoto Yoritimo and Tokugawa Ieyasu. Martial artists also flocked to the shrine and it became increasingly known as the ancestral deity of martial arts. Two famous martial artists mentioned in this connection by the shrine are two ‘sword saints’ Tsukahara Bokuden, 1489 to 1571, and Chiba Shusaku (1792-1855). In the Land Survey of 1688 the shrine was included in the Tokugawa family temple and shrine register and was described as one of the Twelve Ancient Shrines of the Capital 古都古跡12社. I have been unable to find any formal table of the latter.  

The shrine’s main deity, Futsunushi Kami, is often referred to as the Guardian Deity of the Nation. In the Nihon Shoki he is described as a Kami of Military Might. "A” is the operative article here as there are several other such Kami, the most prominent of whom is probably Takemikazuchi-no-Ōkami, and he is the kami at a shrine which was merged into Kameito Katori Jinja.

It was not until quite recent times that the shrine has come to be more widely associated with sport in general.

A festival using that name was soon started and it is still held on May 5 each year.