The term 'FLATTENS, IN THE RING' can be solved by two crossword solutions: KAYOS (5 letters) and KOS (3 letters). KAYOS is a term used in boxing to describe a knockout, when a boxer is knocked unconscious and unable to continue the fight. Kos is a term used in wrestling to describe a pin, when one wrestler holds another down for a certain amount of time. Both terms refer to a situation where one fighter is rendered unable to continue the fight, thus 'flattening' them in the ring.