Captain America: Civil War looks to be one of, if not, the best superhero movies of all time. All of our favorite Marvel characters (minus a few) fighting it out in one epic brawl. Awesome! The story of course is based off the comic storyline of the same name. That story was far different than what it appears this film will be, but the main idea of Cap v. Iron Man is still at the center of this movie. Each of these heroes has their teams. In the comics, Spiderman began on Iron Man's team by dramatically revealing his identity only then to switch to Cap's side later on in the story.
So who switches sides this time? Is it Spiderman again? Maybe Black Panther? I don't think so. The trailer has given it away and no one even saw it happen! Check it out (for the 100th time)!
*SPOILERS TO FOLLOW*
Did you catch it? Let's see if this helps..
Black Widow is standing behind Cap before the epic clash that we've seen a few times in promotion material. Despite it being at the finale of the trailer, we know it's before the battle because Iron Man is clearly seen sitting in a deep state of sadness beside a fallen War Machine with the smoking airport in the background during the trailer. So I don't think he would be coming back to make Underoo jokes, and War Machine is clearly seen standing beside Iron Man in this quick scene. So Black Widow begins on Cap's side...
Then Boom! She's on Iron Man's side, running to face Cap's forces in battle! Black Widow is the one who switches sides. This would be a dramatic turn for her character and would hit Cap hard as she is his closest ally on the original Avenger team.