I'm not aware of "Bring it Down!" as an official Magic: The Gathering keyword or ability. It may be a custom card, a misremembered name, or from an unofficial set—possibly a fan-made or third-party product rather than a Wizards-printed mechanic.
If you encountered this on a specific card, I'd recommend checking the exact card text via Gatherer or Scryfall, since the ability's actual function would be spelled out in reminder text or rules. Real keywords with similar flavor might include things like "Melee," "Battalion," or coordinated-attack triggers, but I don't want to guess at rules for something I can't verify.
If you can share the full card text or where you saw it, I'm happy to walk through how it works and its Commander implications accurately.