Not a whole lot to add here. The guy comes in close, switches from a gun to a combat knife, opponent takes knife, slashes him on his stomach, and throws the knife away with panache.
The video takes this from the point of view of the original knifer, but presumably, you will be able to do this to opponents who get too close to you too. It may seem like a minor detail, but I think this is already one thing Battlefield 4 has over Call of Duty. What say you?