Wall of Caltrops

Oracle Text

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.)

Card Rulings

10/4/2004 Banding is gained when the trigger resolves in the declare blockers step of the combat phase if the criterion is met.