http://www.fangraphs.com/blogs/howard-and-zimmerman-sue-for-defamation-unlikely-to-win/"While filing suit may provide a boost to Howard and Zimmerman in the short-term in their public relations battle against the network, the players are incurring some degree of risk by initiating legal action, and ultimately appear unlikely to prevail in their respective cases."
The article then explains why they are unlikely to win:
"However, under the law, so-called “public figures” — those in the public spotlight, including most professional athletes — are required to meet a higher standard in order to prevail in a defamation case. Rather than merely prove that the defendant made a false statement that hurt their reputation, public figures must instead prove that the wrongdoer acted with “actual malice.”
"...courts usually require that a public figure show that the defendant acted with extreme carelessness, often motivated by some form of ill will towards, or intent to harm, the plaintiff.
"it is interesting to note that the players have only chosen to sue Al Jazeera and two of the reporters involved in the story, rather than Charlie Sly himself. Even though Sly has subsequently retracted his allegations, the players still could have sued him for originally asserting the allegedly defamatory statements. At the same time, though, suing Sly would involve some risk that the pharmacist would be able to produce evidence substantiating his initial allegations, a risk that may have deterred Howard and Zimmerman from suing Sly directly."