Knockout City has been doing surprisingly well for an EA game about dodgeball, this is especially true considering was intended to be free-to-play at first. Thankfully, it looks like the company is trying to walk back its decision to charge for this title by offering trials, free weekend events, and more. But the main reason people stay hooked on this game (outside of the impressively rewarding multiplayer) is for the cosmetics.
And standing near the top of all the cosmetics is the wing back "hologram" that only a special few seem to be able to wear. That said, they're definitely not impossible to get, nor are they some pre-order bonus or something along those lines. The case is that it's not really up to you, but rather the RNG of the game itself.
So, the short answer? It's pure luck.
The Long Answer
To be a bit more specific, the wings cosmetic that keeps popping up on players from time to time (especially those in League Play matches) is actually a Crew Logo. And like most other cosmetics in this game, it’s completely randomized for everyone’s Street Rank unlocks. Luckily, Crew cosmetics are equipable for everyone as soon as any person in the Crew has them unlocked.
Thankfully, because you can invite anyone to your crew, players who have managed to beat the odds early and unlock this logo option have either joined or started Crews that freely invite anyone who want to wear the wings.
What Should I Do?
So to get them yourself, you either have to get incredibly lucky with an unlock or you can do a bit of research online and find one of the groups who freely invite people to their crew, where the wings are set as their Crew Logo.
Alternatively, you could also just play the game until random people you end up playing with invite you to their Crew. But remember, the Crew Logo is set by the Crew Leader, so even if they have the wings, you won't be able to wear them unless the Crew Leader decides everyone should wear them. This isn't exactly an optimal or foolproof solution, it certainly does work if you're looking for the easiest way to nab this particular cosmetic for yourself. Good luck!