[OrangeKing]

I think the difference is in the nature of sports (by which I mean, physical sports) as compared to say, poker or chess or other "mind" games. In sports, there is both a mental and physical aspect. If you understand football completely, but just don't have the physical tools to compete against NFL athletes, you can still share your wisdom with players. In poker, there's just the mental aspect (for the most part - there are other factors too, of course) - if you don't have the proper knowledge, you can't teach, and if you had the proper knowledge, you could play at least reasonably well.

On the other hand, it's not a perfect corelation between playing ability and teaching ability. I'm not too familiar with poker teachers, but some of the best chess teachers are "merely" masters, and not among the best players in the world.