Foster was the second of two first-round picks (No. 31 overall) by the 49ers in last year's draft and started 10 games while registering 72 combined tackles and a pass defensed.
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Foster, 23, a native of Auburn, Ala., was arrested by the Tuscaloosa County Sheriff's Office. He was the highest-graded rookie linebacker this past season. He was sent home from the NFL Scouting Combine after he got into a heated exchange with medical personnel while waiting for his physical.
A former top recruit, Foster shined as an upperclassman for Nick Saban's squad and was named first-team All-SEC while also winning the Butkus Award for the nation's top linebacker in 2016. He then failed a mandatory drug test, which came back as dilute and, per league rules, had to be treated as positive.