(Sport is, of course, the one area of American life where nobody seems
to be agitating for proportional participation; Americans seem content
to let pro sports remain a meritocracy.)

Not true. In baseball, the MLB and it's media have been complaining that baseball is "too white" for a while now---which means "too many" whites and too few successful blacks. Here's Chris Rock on HBO's Real Sports (run by white-hating Bryant Gumbel) in 2015 bitching about baseball being "too white": https://www.youtube.com/wat...

Now the percentage of blacks in baseball has fallen off in recent decades. After integration, Blacks made up 18-19% of MLB players in the 70s, but today they are less than 9%: http://m.mlb.com/news/artic...

Now that's all blamed on whitey somehow, but there are two major things contradicting that. One, the percentage of foreign-born Hispanic players has skyrocketed as MLB clubs have opened camps in the Caribbean and South America; such players are much better behaved and civilized than American blacks, even if the Hispanics have a lot of blacks among them and have weak families. They get along a lot better with whites and yellows who play in MLB and are much more popular; look how Hispanic black David Ortiz became a fan favorite in Boston, and who never had a ghetto moment on camera.

Second, the decline of the black family has meant fewer black fathers around to teach baseball as a father-son rite-of-passage. Baseball may have once been the game of the ruffian poor in the late 19th/early 20th C (especially the rural poor), but by the 1950s and 1960s had become the game of the middle class. Basketball became the game of the broken-homed youth, who came from inner cities, had no fathers, and had less space to set up a sprawling diamond.