Foster was charged with second-degree marijuana possession in Tuscaloosa, home of his alma mater, the University of Alabama. The arrest was later confirmed by the Tuscaloosa Sheriff's office and bond was set at $2,500 for Foster.
The arrest comes nearly two weeks after Foster wrapped up a rookie season in which he finished second on the 49ers in tackles with 72 in 10 games.
Here's a statement from the 49ers: "The San Francisco 49ers organization is aware of the matter involving Reuben Foster and we are now gathering all relevant facts".
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During his senior season at Alabama in 2016, he was named the Butkus Award victor. He was named the NFL Rookie of the Month in November.
Foster also finished the season with the team's highest player grade (90.7), according to Pro Football Focus, just edging second-year defensive tackle DeForest Buckner (90.4).