Defender (This creature can't attack.)
Whenever Wall of Caltrops blocks a creature, if at least one other Wall creature is blocking that creature and no non-Wall creatures are blocking that creature, Wall of Caltrops gains banding until end of turn. (If any creatures with banding you control are blocking a creature, you divide that creature's combat damage, not its controller, among any of the creatures it's being blocked by.)
Banding is gained when the trigger resolves in the declare blockers step of the combat phase if the criterion is met.