Here's input from a guy that played ball at a mixed school although a while ago but maybe it's applicable because I didn't really understand the situation until years later.
Sports, especially football and basketball is an "intimate" activity. I grew up playing with my brothers and friends. In those games you are in close contact with your opponants. You sweat on them and they on you, you hold each other, crash into each other, roll around on the ground, even bleed together.
Frankly, and this will sound quite racist, but I can't stand the smell and the odor of blacks. I know its all un-PC to say something like that but it's absolutly true. I was always grossed out having to have them lean on me all sweaty and stinky, getting that all over me, YUCK, and having to hold and grab them and take them to the ground. God forbid sharing a locker room and towels and stuff.
I know a lot of other white people feel this way. No one will ever admit to it, but is it really surprising? Even if it's not a racial thing it's a cultural thing. So what's the difference?
I would hope that blacks feel the same way about whites so it would encourage them to stay away. But it seems to me that they crave physical closeness with whites. There were black guys that I played with that were all over me and the other white guys. And we all know how much they like white women. Once when I was younger I was with a black girl, she was pretty but....all I can say is, it will never, EVER, happen again.
A person can't pick which things make them feel uncomfortable and which they don't like, which smells and sights, etc. It doesn't mean that blacks are "inferior" or bad, it just means (to me) that they are different.
This has been the way that people have felt for centuries. The current paradigm states that we are all the same. SURPRISE! It's not true.
I think that at some level white kids do not want to be with blacks in any kind of close quarters. They can't say why of course. That kind of truth is not allowed, but they can stay away. And they do. Good for them. If mixing is something they do not want to do then I totally support it.
To be honest I have no idea why any white man plays in the NFL. It must be torture.
BTW I have not mentioned the unwanted social interaction. I hated black athletes, they are even stupider and more assine then the rest of the demographic. That alone would be enough to avoid interaction. I am assuming that anyone of intelligence here understands that the reason white kids hang with other white kids and black kids hang with other black kids is because they can't stand each others company in social situations. That all should be obvious to anyone here but I thought it important to point out another important reason for self segregation in the athletic arena.