Right Enforcement?

[VALJ]

Both A and B players can legally BBW if all players involved are in the FBZ and on their LOS at the snap, as long as contact is in the FBZ before the zone goes away. Clipping is legally permitted only by A linemen on the LOS and in the zone on B players on the LOS and in the zone, if contact is in the FBZ before it vanishes. Blocking in the back is legally permitted only for A players on the LOS and in the zone on any B player in the zone at the time of the snap, if contact is in the FBZ before it vanishes.

The key difference between clipping and BIB is that only defensive players in the FBZ and on their LOS can be clipped, but any defensive player in the FBZ - whether on the LOS or not - can be legally BIBed. They key difference between those two and BBW is that a B player can legally BBW, but he can't legally clip or BIB.