Does banding still exist in Magic and how does it interact with trample?

Banding is a keyword ability that has not appeared on new cards in decades but remains fully defined in the Comprehensive Rules (CR 702.22). Several old cards like Benalish Hero and Wall of Shields still carry it, and it is legal in formats where those cards are legal.

The core of banding is about combat damage assignment. Normally, when a creature with trample attacks and is blocked, its controller assigns lethal damage to blockers and sends the rest to the defending player (CR 702.19b). Banding disrupts this by transferring damage-assignment control. Specifically, CR 702.22j states that when a creature with banding is blocked, the defending player — not the attacking player — chooses how the blockers' damage is assigned; and CR 702.22k states that the defending player chooses how the attacking band's damage is divided among blockers.

This matters for trample because trample's excess-damage rule only applies when the attacking creature's controller assigns damage (CR 702.19b). If the defending player takes over damage assignment for the blocked band, trample's mechanic is effectively neutralized — all damage must be assigned to blockers as the defending player sees fit, and no damage spills over to the defending player or planeswalker.

Concrete example: Your opponent attacks with a 6/6 trampler. You block it with your 1/1 Benalish Hero (which has banding). Because a banding creature is in the block, you (the defending player) now assign the 6/6's combat damage. You assign all 6 damage to your own 1/1 — yes, even overkill — and zero damage reaches you. The trampler's trample ability cannot override your assignment control granted by banding.

In summary: banding is a legal, functional ability. When it causes the defending player to control damage assignment, trample loses its signature ability to punch through excess damage, making banding one of the only mechanics that hard-counters trample in combat.