The Winter Soldier

Joe and Anthony Russo are also the ones who directed (and made a hit out of) Captain America: The Winter soldier. They are the ones responsible for resurrecting Steve Roger's past "“ in the form of his childhood friend Bucky Barnes, MIA in WWII and believed dead, returned as an assassin for the foes the Captain fought during the second WW.

Talking about the scene which was also seen in the credits of Ant-Man the directors say that it doesn't happen too early in the film "“ and this is understandable. Most likely, the beginning of Captain America: Civil War will feature the African Market battle, which leads to the Sokovia Accords. And since Crossbones is the one leading the assault, this would work as frame-up "“ everybody will believe that the Winter Soldier is behind it all (everybody except Steve and his friends).

According to Joe Russo, the man trapped in the vice (most likely by Steve and Sam) is not Bucky and is not the Winter Soldier "“ it is someone in-between. By focusing on this friendship, the idea was to emphasize the fact that Captain America: Civil War is not an Avengers flick (though it is called that way by many fans).

Anthony Russo, on the other hand, says that this new character is still caught by the past "“ both as a friend of Steve and as a HYDRA assassin. And this brings him right in the middle of the Civil War "“ which, maybe, means that Bucky will indeed be framed as a new leader of HYDRA, thus having the governments of the world, as well as the Iron Man faction of the Avengers, on his trail.