Funny that this topic should come up when SI had a article on this so recently.
http://sportsillustrated.cnn.com/2007/baseball/mlb/specials/spring_training/2007/03/14/sabathia.race.ap/index.html When I read this article I really didn't know what the answer was. There are so many ways to view this issue of falling participation by african-american kids in baseball. Is it an ethnic thing? Is it a cultural thing? Is it economic? Though there is a tendency to divide people into groups racially in the US is this really an accurate method of analysis when examining the issue at hand? Is a black inner city kid equivalent to a black middle class kid in terms of interests, economics, opportunities, peer groups, and availibility of safe areas for play? Probably not. I would suspect that race or ethnicity is less a factor than economics or location (inner city vs suburbs). I would venture to guess that, for instance, middle class kids of all races/ethnicities (or whatever other label you wish to apply) would have more in common with other middle class kids than with kids of the same race/ethnicity that live in areas that are more challenged economically.
Working in an ER I see lots of kids with athletic injuries. I also work in an economically depressed part of town that is where "black", "mexican", and "white" areas of town converge. I see lots of poor kids participating in baseball (and other sports). But it seems that participation is more along the lines of kids who live in structured family units and those that do not. It seems (strictly from observation) that kids that live in households with both mother and father figures (whether they are blended families or not) seem to participate more in sports (and do so as a focus of family life) than those who do not. Where there seems to be a lack of participation is amongst those children who have a very loose, or in some cases nearly nonexistent, family structure. Often these kids have one custodial parent, may sleep in different places on consecutive nights (ie between parents' homes or grandparents') and often have various siblings with different parents than themselves. Their parents tend to be quite young and they often are the second or third generation with such a loose family structure. There really isn't any racial or ethnic division here. Family 'culture' seems to be a larger issue.
I will say that basketball is played by huge numbers of kids (and by a lot of guys well into their twenties) and is usually done so informally (I can't count how many dislocated shoulders and ankle injuries I've seen amongst basketball players playing informally in the evening). This is also San Antonio so our only big-league franchise is a basketball franchise. Baseball and all other sports are usually played in structured leagues. Most of these are also school based leagues with the exception of baseball/softball, which of course has little leagues, and football which has its Pop Warner leagues. It does seem that the kids who come from less structured family units and play sports in organized leagues usually do so in school based leagues.