Hitch was beaten by local thugs affiliated with the crazy Syrian Social Nationalist Party, an either left- or right-wing group wishing to see basically all of the middle east joined as "Greater Syria." All because—like our very own Poster Boy!—he defaced a poster. Unfortunately it was a poster for the SSNP, and Hitch defaced it by writing "Fuck the SSNP" on it (that's the kind of brilliant rhetoric he's famous for) and there were some SSNP members right across the street, and they beat him up. According to this blog, "he is still walking with a limp."
According to this awesome blog, it's because Hitch was at the wrong bar, in the wrong neighborhood.