Aldon Smith was reportedly arrested, again ... after allegedly violating an order that barred him from contacting the alleged victim in his domestic violence case.
Smith turned himself in this morning after San Francisco PD issued a warrant for his arrest, according to a San Francisco Chronicle reporter.
We broke the story ... the former NFL star had been arrested and charged with 4 misdemeanors -- including domestic violence -- after allegedly beating up his fiancee on March 3rd.
At the time of the incident .