Research by scholars at four separate universities, published in the American Economic Review, analyzed 3.5 million pitches thrown in Major League baseball games from 2004 to 2008. The study concludes that black and other minority pitchers get less strike calls than white pitchers. As a result, the study shows that minority pitchers compensate for this bias by throwing balls closer to the middle of the strike zone in order to get favorable calls. This, in turn, hurts their overall performance because they are offering pitches that are easier for batters to hit.
The full article can be accessed here.