Raging River is a rare Enchantment card from Collectors' Edition (CED), collector number 169. Current market price: $29.99, TCGplayer market prices via Scryfall.
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.