What's unique about Quake III Arena, as it relates to AI, is that the notion of capture the flag gameplay is a team-based sport that seemingly requires human traits to be effective at. Attacking and defending are critical elements, and it all hinges on effective teamwork to be successful. Apparently, though, computers can be good at this as well.
The researchers note that though AI agents have been getting better at two-player games, real-world problems that AI might be useful for (i.e., not just gaming) require teamwork. So, they designed a computer program that excels at one particular type, that being the capture the flag mode in Quake III Arena.
"The agents were trained by playing thousands of games, gradually learning successful strategies not unlike those favored by their human counterparts. Computer agents competed successfully against humans even when their reaction times were slowed to match those of humans," the researchers wrote.
The paper is a long read and goes into great detail on the technologies and training methods involved. Part of it entails repetition. By playing a game repeatedly, an AI agent can learn which strategies lead to success and which ones lend themselves to unfavorable outcomes, and adapt accordingly.
That's grossly oversimplifying things, of course, but the takeaway is that machines can learn to work together as a team, with the right training. That in and of itself leads to some interesting questions.
"How you define teamwork is not something I want to tackle," said Max Jaderberg, a DeepMind researcher who worked on the project. "But one agent will sit in the opponent’s base camp, waiting for the flag to appear, and that is only possible if it is relying on its teammates."