Raging River [Beta Edition]

Set: Beta Edition Type: Enchantment Rarity: Rare Cost: {R}{R} Whenever one or more creatures you control attack, each defending player divides all creatures without flying they control into a "left" pile and a "right" pile. Then, for each attacking creature you control, choose "left" or "right." That creature can't be blocked this combat except by creatures with flying and creatures in a pile with the chosen label.