RIO DE JANEIRO, June 15 (Reuters) - Police blocked a small group of anti-World Cup protesters who were trying to reach the Maracana stadium in Rio de Janeiro on Sunday, before Argentina played Bosnia in the city's first game of the tournament.About 150 bandanna-clad protesters carrying banners that said "Fifa go home" marched towards the stadium, causing some stores to shut their doors temporarily and one metro station to close briefly.Police mounted on horseback formed lines to block the group's path to the stadium.