Per ESPN's Adam Schefter, Smith's discipline is for violating the league's personal conduct policy.
The Athletic's Jeff Zrebiec reported Aug. 20 that Smith violated the league's personal conduct policy. Zrebiec added the nature of the violation was unknown but pointed to a report by the Baltimore Sun's Jeff Barker in November 2017 outlining "allegations of illegal drug use and domestic violence."
Micaela Sanchez, the mother of Smith's three-year-old son, alleged he had gotten physical with her and used drugs with his son present. Smith denied the allegations.
"There's no truth to it," he said. "I'm not going to give the story any legs."
According to Zrebiec, the Ravens had been "bracing for a multiweek suspension," so Tuesday's news won't come as a massive surprise to the team. Smith will be eligible to return for the Ravens' Week 5 matchup with the Cleveland Browns on Oct. 7.
This is the second straight season in which the NFL suspended Smith. He served a four-game ban starting in December 2017 for a performance-enhancing drug violation. The suspension came shortly after Smith suffered a season-ending Achilles injury.
Smith appeared in 12 games last year, making 28 combined tackles and intercepting three passes.
The 30-year-old ranked second in Bleacher Report's NFL1000 year-end ranking of the best outside cornerbacks.
"Injures have limited his top-level speed, but few defenders in the NFL have a better sense of route recognition, and Smith has the mental edge to succeed in any defense," Bleacher Report's Doug Farrar wrote. "If health is a skill, it's the only one he hasn't fully shown in his pro career."
Baltimore allowed the 10th-fewest passing yards in the NFL a year ago (213.8 yards per game). In the final four games of the regular season—when Smith was out injured/suspended—the Ravens surrendered 1,038 yards and six touchdowns through the air.
While Smith's injury wasn't solely to blame, the Ravens went 2-2 to close the year, losing out on the playoffs via a tiebreaker with the Buffalo Bills.
The pressure will be on Tavon Young and Marlon Humphrey to help Baltimore get off to a good start in 2018 in Smith's absence.