Doubtful. My intuitive model is that those who do play sport and receive brain damage are less likely to end up in places of risk. Where enough people play sport and don't get head damage and do get jobs in high-powered places.

While there would be some; I imagine not many people fall into the problem category. If anything - the things that competitive sport teaches about competition and teamwork as well as "trying hard" would probably outweigh a bit of brain damage. while "not having brain damage" is obviously better than "having brain damage", maybe the trade off can be useful? (is useful - given that people still value sport in this way)