"Gates yelled at the officer, refused to calm down and behaved in a tumultuous" manner." That's why he was arrested. Not because he is black.
None of which was arrestable behaviour after he had proved that he was the owner of the house.
That's patently ridiculous. If you are uncivil you are breaching the peace. Hence, he was arrested.
according to one version..
another is..
Gates denies that he yelled at the officer, other than to repeatedly ask his name and badge number, and says he readily turned over his driver's license and Harvard ID to prove his residence and identity
we might never know the truth and frankly the truth might be some place in between.
but, there is a reason the story is carrying so much weight across the country.
boston and the surrounding area has had its own nasty history of racism that goes to pretty current times.
the reaction to busing was as nasty as some places in the south.
and more recently..
Stuart caused a citywide manhunt in 1989 when he said a hooded black man shot him and his pregnant wife as they got into their car after a maternity class. Stuart eventually was labeled the killer, but not before a black man arrested on unrelated charges became the prime suspect.
the above and more from this ap article that gives a lot of background
on the situation.