This sequence comes courtesy of Captain America: Civil War's storyboard artist Darrin Denlinger, whose other Marvel projects include Iron Man 3, Captain America: The Winter Soldier and Avengers: Age of Ultron. The scene starts out with Ant-Man and Captain America pulling the old "enlarge the truck" attack on War Machine and Black Panther. Captain America and Ant-Man then make a run for it and agree to rendezvous later. Ant-Man shrinks down and gets a ride out on one of his flying ant allies, but Cap is soon stopped by Black Widow. The fight has a lot of rhythmic beats: Cap blocking her projectiles with his shield, Black Widow breaking out her electric gauntlets, her stealing Cap's shield, etc.

Eventually they have a similar encounter to the one they had in the movie outside of one of the hangars, where Natasha Romanoff asks Steve Rogers if he's ever going to stop. Just like in the theatrical cut, Steve says no. Soon after, he asks if she brought her gear, and when she respond affirmatively, he tosses her off the building, leaving her to break out her grapple gun and uses its hook to break her fall. Even when feuding with his friends, Captain America still wants to make sure his friends are okay.

Although Black Widow joined Team Iron Man in Captain America: Civil War, there were several instances where she tried to look out for Steve Rogers and make sure he wouldn't get hurt or captured. We get a hint of that in this storyboard sequence, but she hasn't reached the stage where she betrays her fellow pro-registration allies. By the end of the finalized fight, Natasha allowed Steve and Bucky Barnes to flee and track down Helmut Zemo in Russia. As of the end of the movie, Black Widow is in the wind, and while it wasn't explicitly said that she was working with the other anti-registration heroes now, she's definitely a fugitive from the law. Oh well, at least she and Cap won't have to fight anymore.

Captain America: Civil War is still playing in theaters, and while Black Widow's involvement in Avengers: Infinity War hasn't been made official yet, it seems likely that her and Captain America will reunite during the two-part epic.