I know it's not the gospel, but I often look to the Reddings Study Guide for assistance. On this subject, in the 2021 Addendum to the 2020 Guide, it says "[e]ven though a lineman is in the zone, if he rises or takes a step back at the snap, he cannot block low. He may take a forward or lateral step as he lowers his torso to initiate the block. He may then take a second step as he initiates the contact. If the contact is not made by the completion of the second step, the block is illegal. In most cases, a block of a head-to-head opponent will be legal. A block of an opponent lined up in the adjacent gap or opposite an adjacent teammate in the zone may be legal in a normal offensive formation; however, if the offensive formation has wide splits, the block is likely illegal. The initiation of the block and the contact must be a continuous motion." I think this description of a legal BBW in the FBZ is helpful, and seems consistent with the added language of subsection (c) in Rule 2-17-2.