I know very little about sports, Japanese or otherwise, so perhaps I shouldn't comment, but I recall that at Sumo matches there were ritual singings of Kimigayo. Anyhow, the issue of Kimigayo & Hinomaru has had less to do with sporting events than with the struggles between the Japanese Teachers Union [Nikyoso] and the Ministry of Education [Monbusyo]. The government has wanted to impose nationalistic rituals at sotsugyoshiki [graduation ceremonies] and nyugakushiki [matriculation ceremonies], whereas Nikyoso, whose leaders have been left-wingers (some of them Communists), has resisted nationalism.
BTW, the lyrics of Kimigayo has nothing to say about the Japanese as a "people." It's in fact a praise song for absolute monarchy (composed in 1880 at the request of the Naval Ministry):
***** Kimi ga yo wa Chiyo ni yachiyo ni Sazare ishi no Iwao to nari te Koke no musu made
[Thousands of years of happy reign be thine; Rule on, my lord, till what are pebbles now By age united to mighty rocks shall grow Whose venerable sides the moss doth line.
Trans. Basil H. Chamberlain]
(Kodansha Encyclopedia of Japan, Vol. 5, p. 336) *****
As you recall, modernity in Japan began with a supremely reactionary _and_ nominalist gesture: the nominal "restoration" of Tenno [emperor] as the symbolic figure of authority, though real power, of course, rested in the hands of the modernizing state builders & rising bourgeoisie. The French are lucky that they got "La Marseillaise," which is a song of revolution. Aux armes citoyens!
Yoshie