A1 is dribbling near the sideline when B1 obtains legal guarding position. B1 stays in the path of A1 but in doing so has
(a) one foot touching the sideline or
(b) one foot in the air over the out-of-bounds area when A1 contacts B1 in the torso.
(a), a blocking foul is ruled on B1 because a player may not be out of bounds and obtain or maintain legal guarding position. In
(b), a player-control foul is ruled on A1 because B2 had obtained and maintained legal guarding position.