The hybrid nature of modern NFL defenses requires players to do more than ever, and defensive ends are no exception. It's the rare 4-3 end who stays in one place for every snap of a game, let alone every snap of a season. Now, they may line up in two-end sets to one side, forcing guards to act like tackles and causing all kinds of confusion along the offensive line.
More prominently, defensive ends, trained as edge-rushers, must become conversant with the idea of moving inside on obvious passing downs when teams move to nickel and dime defenses.