Bam's older brother, Anthony, is a redshirt freshman defensive lineman for the Terps.
He previously committed to LSU in December.
The three-star product joins the Terps from nearby St. John's College High School.
Lewandowski racked up 2,804 yards and 28 touchdowns in 10 games for Wisconsin-La Crosse last season.
Bradley is Maryland's 11th recruit — all of whom hail from Maryland, Washington D.C. or Virginia.
The Gaithersburg native becomes the Terps' highest-rated class of 2021 recruit.
Smart is Maryland's second 2020 commit, joining three-star Marcus Dockery.
Defensive back Osita Smith, offensive lineman Amelio Moran and defensive lineman Almosse Titi all signed Wednesday.
The Terps added two recruits to their 2021 class and one to their 2020 class.
Among other signings, coach Mike Locksley secured five-star wideout Rakim Jarrett.