Professional athletes should join the ranks of high-profile celebrities who have come out in support of social justice. They have enormous fanbases, not to mention enormous amounts of money. Both of these factors mean that they have incredible amounts of influence that they should use for good by encouraging more social justice to take place.
Appreciating the financing of the professional athletes as a group, I would appreciate them taking a position as a social activist. They already have the media coverage and a following. They can be a force for good social change and lead by example themselves. Pat Tillman is a wonderful example of a social activist and a hero to many. Glen Coffee is another memorable social activist/athlete.
Professional athletes can used their considerable influence to help do good and create social changes. Because people look up to and follow professional athletes so closely, they arguably have the most influence when it comes to social causes and changes. This means they have the most potential to do good.
Professional athletes do not enter their field to make social comments. They do it to because the are good at it and they want to be the best they can and hopefully earn money doing it. If they want to make use their influence and fame to enhance a social cause they feel strongly about, it is likely that they will have a big influence as they are often in the public eye. However in doing so, they run the risk of ruining their existing career if things go wrong. Not all press is good press.