Which hand or game was this? Why DN raised 86s in position is hard to say in the abstract; why anyone might want to do this would depend on game-specific conditions. How many people entered the pot before him (if any)? Who were these players? What sorts of tendencies did they exhibit prior to this hand? DN may have been making a squeeze play, isolating a fish, punishing limpers, or a combination of these things... or he may have had a different purpose for his play altogether.