The Duel at the New Avengers Facility was a planned theft for the Signal Decoy located in the New Avengers Facility that escalated to a brief skirmish when Ant-Man was discovered by Falcon. While the duel was a minor confrontation at the time, it proved significant when it made Ant-Man's presence known to Falcon who would subsequently recruit him into the Avengers Civil War.
Preparing to steal the Yellowjacket Suit from Darren Cross, Hank Pym, Hope van Dyne, and Scott Lang planned to visit one of the warehouses owned by Howard Stark to steal the Signal Decoy. Upon arriving, they discovered that after the Battle of Sokovia, the warehouse was rebuilt, and became the New Avengers Facility. Sam Wilson was one of the members recruited by Captain America to the Avengers; the New Avengers Facility is the Avengers' training facility.
As Scott Lang arrived at the facility, he chastised Hank Pym for not disclosing that the warehouse was the New Avengers Facility, although this information came as news to Pym as well. As Lang stayed ant-sized, Falcon arrived, having detected an unknown signal on the perimeter. Realizing that Falcon's Combat Goggles negated his ability to hide by remaining shrunken, Lang returned to normal size and introduced himself, hoping to maybe get Falcon's help, only for Falcon to attempt to detain him for trespassing.
Lang shrank and maneuvered around the open ground, changing size while fighting Falcon and dodging his gunfire. Riding Ant-thony, Lang lured Falcon into the storage bay, successfully shrinking the device he wanted, and made his way into the wiring of the flight pack of the EXO-7 Falcon to ground Wilson and disable the sensors that allowed him to detect him when shrunken. Lang escaped and Wilson radioed Natasha Romanoff at the base and told her not to tell Captain America about his defeat to a shrinking man.
Ant-Man used the Signal Decoy to help in his battle with Darren Cross. Word even got around to HYDRA about the benefits of shrinking technology against an Avenger. Though slightly embarrassed, Falcon was also impressed with the skill demonstrated by Ant-Man and sought to have him recruited. Luis, a friend of Scott Lang, told Lang that Falcon wanted him.
When Falcon and Captain America learned that someone was planning to unleash HYDRA's Winter Soldiers, Falcon suggested calling Ant-Man for assistance. Prior to the Clash of the Avengers, Lang apologized to Wilson for the incident. Wilson held no grudge and said it was a good audition, but promised him it would not happen again.