In today's New York Times, numbers guru Alan Schwarz discusses a paper by Joe Price and Justin Wolfers on referee decisions in the NBA. Price and Wolfers find a subtle racial bias in referee decisions - black players get called for about .1 to .2 more fouls per 48 minutes played. This effect is not one of large magnitude, but it is robust across the specifications that Price and Wolfers examine. The NBA has done their own follow-up study and claims otherwise, (the Price and Wolfers paper has been around for a year), but won't release the data.
Update: This wire story has some sharp criticism of the Price and Wolfers paper, by an NBA representative.