Just because someone is good at a sport doesn't make them good at coaching. The sooner someone gets out of playing a sport, the sooner they get into coaching, generally, giving them more experience and building their resume. Someone with less physical talents will probably get out of the sport sooner, or depend on their knowledge of the game opposed to their physical traits, making them better at coaching, in theory.

At every advancement in the sport (high school -> college -> NFL) there is an increasing representation of black people, and a decreasing representation of white people, meaning more white people are entering the prospective coaching career field. Looking at just the NFL and College and saying there are X amount of black players, there should be X amount of black coaches is dumb.

Just look at the NFL coaches, how many of them took any meaningful snaps as NFL players? Mike Vrabel and... that's it I think. Most coaches were guys who were good enough to maybe get drafter but not start, at best, and generally fizzled out in college. Then they became graduate assistants, or similar type jobs. Stars don't generally want to become a graduate assistant after being the hot name on campus in college, they're not ready to give up their NFL dream, might go play in whatever XFL knockoff starts that year, CFL, etc. The guy that knew he was never going to play in the NFL is probably going to take a graduate assistant job for next to nothing.

This is where I think racism comes in, although it's more the socioeconomic stuff - the white kid who fizzled out in college is more likely to come from a background allowing him to take the graduate assistant job for a couple bucks, and this was probably his plan all along. The black kid who fizzled out all the same is more likely to need some more money and won't be able to basically work for free, or other reasons he won't get the job because of his upbringing, or was depending on the NFL since he's been the top 1% up until this point. I think this is the point where we see a real difference between white and black coaches starting, by the time it trickles up to the NFL level, it's too late.