August 31, 2004 -- A cop was in serious condition with head injuries today after he was knocked off his scooter and stomped by protestors at an illegal march, police said. Several thousand people took part in the march — conducted without a permit by the group Poor People's Economic Human Rights Campaign — which started at the United Nations, then moved south on Second Avenue, west on 23rd Street and back uptown on Eighth Avenue. The violence happened at 30th Street and Eighth Avenue, where police barricades were set up to protect Madison Square Garden. Police spokesman Paul Browne,...