9:34 AM PT -- San Francisco PD tells TMZ Sports ... Earlier this week SFPD’s Special Victims Unit investigators obtained information that Mr. Smith violated a domestic violence restraining order stemming from an incident that occurred on March 3, 2018.

A warrant was issued for Mr. Smith’s arrest. The Department worked with Mr. Smith’s legal counsel to arrange a date for Mr. Smith surrender himself.

This morning Mr. Smith, surrendered himself to SVU investigators and will be processed for the warrant and three counts of misdemeanor violation of a protective/stay away order.

Aldon Smith was 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.

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 3.

At the time of the incident ... a protective order was issued that banned Smith from having any sort of contact with his accuser.

AS allegedly violated that order ... promoting officials to issue the warrant.

Smith turned himself in Friday morning.