The Los Angeles County district attorney's office says Smith pleaded guilty Tuesday to a felony assault charge. He was also sentenced to five years of probation and was taken into custody after the court hearing.
Prosecutors said the cornerback beat his sister's boyfriend after the man tried to intervene in an argument between Smith and his sister.
They said he stomped on the man's head, causing "serious bodily injury."
The Raiders released Smith on Monday.
The former University of Utah star played for Miami from 2009 to '12 and Kansas City from 2013 to '15.