Captain America: Civil War was easily one of the brightest spots in what was a humdrum summer thanks to its big character moments, years worth of payoff, and epic superhero on superhero action. The fight at the airport between Team Cap and Team Iron Man is chock full of character based action and fan pleasing moments, many of which comes from Paul Rudd's Ant-Man. The new guy on the block got some of the best moments of the whole sequence, but early versions of the script might have changed all that by siding him with Iron Man.
This is concept art from the Twitter of Marvel Studios Visual Development Supervisor Andy Park, and shows Ant-Man locked in combat with Hawkeye. The two heroes were on the same team in the final movie, but originally Scott Lang was going to be a part of Iron Man's squad. The thing to remember about concept art is that it's done very early in the game in order to help visualize and set the aesthetic of the film. Sometimes it doesn't reflect the final film - especially with blockbusters, which tend to change a lot in the development process. Still, it provides an interesting window into the many shades of filmmaking.
Side note: see that person firing a gun in the background of the picture? Pretty sure that's Sharon Carter. In earlier versions of the script, Sharon had a more active role and actually participated in the big fight. It's pretty easy to see why she was cut from the fight entirely, giving that she isn't a super person and shooting superheroes is a bit extreme. Or its just Bucky.
Ant-Man was a character that really could have gone on either team. It's not too hard to see why signing the Sokovia Accords would be a good option for an ex-criminal with a family to think about. On the other hand, Scott Lang is pretty anti-establishment and he already has connections to Cap thanks to his run-in with Falcon. However, if Ant-Man had joined up with Iron Man then it probably would have deprived us of one of the most wanted and geekiest moments in the entire film: Ant-Man riding Hawkeye's arrow. You can't really do that if they aren't on the same team.
Ant-Man has some of the best bits in the entire fight right, there next to Spider-Man. Check out this compilation of some of his biggest moments, which of course includes him becoming Giant-Man.
Barring any cameos, you can most likely next see Scott Lang in Ant-Man and the Wasp, which is scheduled for release on July 6, 2018.