I think racism is about power - sorry to sound Marxist, but I think the Marxist interpretation carries a lot of weight. If we can separate ourselves over something, it allows us to hold others down and be succesful ourselves, whether its class (as Marx argued), race, gender, height, weight, whatever, people will find differences that makes themselves into a group - to claim an African-American coach is inferior to a caucasian coach of course is wrong, racist, and ungrounded, BUT many people do think that way, because it enhances the superiority of their race, or if you are of that race, may become a self fulfilling prophecy.
that said, I understand why people use race to put others down, I hate that it happens, I wish we lived in a color-blind world, but the fact remains we don't. I think it is ok to embrace our differences, as long as it doesn't get in the way of us being one nation