The term 'Did a Jackknife' is a phrase used to describe a type of dive. It is a move in which the diver enters the water with their arms and legs spread wide, then brings them together in a sharp, knife-like motion. The term comes from the similar motion of a jackknife folding knife. The crossword solution for this term is 'Dove', which is another type of dive in which the diver enters the water with their arms and legs tucked close to their body.