According to "Horyakukanki" (A History Book of the 14 century in Japan), the cause of the Shimotsuki Incident was that TAIRA no Yoritsuna gave a slander that the Adachi clan conspired a rebellion to become Shogun, as Munekage changed his name into MINAMOTO, saying that his grand-grandfather, Kagemori ADACHI was an illegitimate child of MINAMOTO no Yoritomo.
『保暦間記』によれば、霜月騒動の原因は、宗景が曾祖父の安達景盛が源頼朝の落胤であると称して源氏に改姓したところ、平頼綱が安達氏が謀反を企んで将軍になろうとしている、と讒言したためとしている。