Starting off with one of the more basic scenarios, the idea here is pretty simple: Spider-Man joins Bucky, Scarlet Witch, Hawkeye, Ant-Man, and Falcon on Team Cap, aligning himself with the First Avenger. This movie is an ideological battle (because they're very much en vogue when it comes to comic book stories this year), with Steve Rogers and the rest of his team opposed to the idea of government regulation of superheroes, or The Sokovia Accords. Peter Parker, then, an impressionable teen, believes that is the right stance to take, and as his fledgling hero career gets underway, he teams up with someone who is very much a recognisable symbol of truth and justice in the USA, Captain America. There's also the fact that he's given an off-hand mention in Ant-Man, who is on Cap's team, which could lend itself to the notion of them being aware of him, and recruiting him for their team.