The Outriders are a mindless species of aliens subservient to Thanos and the Black Order, used to fight in the Battle of Wakanda. The Outriders were deployed in Thanos and the Black Order's assault on Earth, specifically in their attempt to retrieve the Mind Stone from Wakanda.
Several Dropships were released from Sanctuary II and were sent crashing down in and around Wakanda; the doors opened and the Outriders were unleashed upon the African plains.
Along with the Black Order, the Outriders faced the Wakandan army and Captain America's Avengers faction, throwing themselves at the force field in an attempt to destroy it. Many are killed, but as they continue, the force field begins to falter.
When some begin to circle around the force field, the Wakandans are forced to let them through, prompting the aforementioned army and faction to engage. As the two sides battle, the remaining Black Order, Corvus Glaive, Proxima Midnight, and Cull Obsidian, attack Vision, Scarlet Witch, and the Hulkbuster. Meanwhile, the Outriders are refusing to be bested by their opponents, relentlessly continuing their assault.
Soon afterwards, as the heroes are beginning to be worn down, Thor, Rocket Raccoon, and Groot join the battle, greatly turning the tide. Some Outriders attempt to escape, although most are decimated by the Wakandans and the heroes.