Ravens general manager Ozzie Newsome says the violation occurred while Williams was playing for the Tennessee Titans. Williams was with the Titans in 2008 and at the outset of last season before joining the Ravens in November.
"We were aware of this" before Baltimore signed Williams, Newsome said Thursday.
The 25-year-old Williams was taken in the seventh round of the 2008 draft by Tennessee. He played one game with the Titans in 2008, and last year he played in four games with Tennessee and five with Baltimore.
He will compete to play nickel back when training camp opens next week.