I'm sure there are a few famous black athletes today who are Republicans. Gaining financial success in the private sector can be a big factor in changing someone's political orientation.
Jesse Owens, one of the greatest Olympic athletes ever, was a known Republican and suffered an income tax case brought against him by the Franklin D. Roosevelt administration, believed by some to have been politically motivated. Jackie Robinson (perhaps the best known black athlete in American history as the man who desegregated major league baseball) was a RINOish Republican, a good friend of Nelson Rockefeller. And the great basketball player Wilt Chamberlain was a Republican as well, IIRC. More recently, Lynn Swann, a former pro football star, ran for statewide office in PA in 2006 as a Republican and was defeated.
I heard the Williams sisters (tennis) were Republican.
Lots of NBA stars fundraise for Osama though.
Charles Barley used to be a RINO but switched to Leninist several years ago.